“We basically have three choices: mitigation, adaptation and suffering. We’re going to do some of each. The question is what the mix is going to be. The more mitigation [(reduction of emissions)] we do, the less adaptation will be required and the less suffering there will be.”

Professor John Holdren, former President of the American Association for the Advancement of Science

How hot is too hot? The promises of the Paris Agreement

In an attempt to limit the dangers of climate change, in 2016 the United Nations Framework Convention on Climate Change drew up the Paris Agreement. It came after 25 long years of fractured climate negotiations and was based on the very latest scientific research that showed that the previous target – to limit global heating to 2°C above pre-industrial levels – was not “safe”. The purpose of the Paris Agreement was therefore to commit the signing countries to “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change”. To date, a total of 189 countries have given their formal consent to the agreement, as well as the European Union.

Whilst committing to keeping heating “well below 2°C” was certainly a monumental step forwards, it is important to realise that we should be aiming much much lower than that. Indeed, we are already seeing enormous impacts of climate change at just 1°C of heating (see section on what’s already happening to our planet as a result of warming and why). The risks increase with every fraction of a degree. Even if we manage to limit heating to 1.5°C this still comes with huge risks. In particular, this amount of heating will be absolutely devastating to some parts of the global south. However, given the appalling lack of adequate action to date, limiting global heating to 1.5°C is really the very most we can hope for right now.

Yet it is now 2020 and in the five years since the Paris Agreement was signed we have seen precious little action at the scale required to keep to the 2°C limit, let alone the 1.5°C one. And we do not have long left to act.

How hot is it likely to get and when?

“Should we continue as a planet to increase greenhouse gases as we have done for the past two years and as we have done for the past 150 years, we would way exceed the 2°C maximum temperature rise and certainly the 1.5°C. What that means is that future generations will have to live in a world that is so unstable that it will be very difficult for them to have any predictability about their life whatsoever.”

Christiana Figueres, former United Nations’ Climate Chief, February 2019

One of the ways that scientists predict how much the Earth will heat up in the future is by using climate models. Climate models are massive computer programs which take the best physical understanding and observations of the real world and use them to simulate how the world’s atmosphere, oceans and ice sheets will change in response to different levels of greenhouse gases in the atmosphere. One of the key roles of the Intergovernmental Panel on Climate Change (IPCC) is to combine the results from all the different climate models and then use them to make estimates of how the Earth’s temperature and climate will change in the future.

At our current rate of warming, even with all the government policies and pledges in place, the IPCC warns that we will pass 1.5°C of heating some time between 2030 and 2052, probably around 2040. This means that we’ll be sailing past 2°C of heating – the amount of heating the 189 countries who signed the Paris Agreement committed to staying “well below” – by around 2060.

However, it is likely that global heating will actually occur even faster than this. In a recent piece in Nature, it was argued that our current emissions pathway makes it most probable that we will hit 1.5°C heating by 2030 and 2°C heating by 2045.

In the absolute worst case scenario, if emissions keep increasing and it turns out that the Earth’s climate is even more sensitive to changes in greenhouse gas levels that was previously thought, we could be heading over 2°C heating even sooner, perhaps even as early as 2035.

The impacts of a 2°C world would be devastating – see section on what our world will look like by 2050 if we don’t take radical action now. But, if we keep emitting greenhouse gases, heating won’t stop there. It will only cease when we succeed in stopping all carbon emissions.

Even taking into account all climate policies that were already in place in December 2019, by the end of the century we are likely to be heading towards an average global heating of 3°C. Given that we can’t predict the climate perfectly and that countries might backtrack on their promises, there remains a significant chance of us going over 4°C heating. A 3°C hotter world would be an absolutely catastrophic outcome. A 4°C hotter world would be even more so. (See section on what our world will look like by the end of the century.)

But what about all the promises that governments have made? The thing is, even if governments don’t just stick to their current policies, but also honour all the additional pledges and targets they have made (a situation that has proven time and again not to happen), we are still heading towards around 2.6°C of heating by the end of the century – with a one in three chance of going over 3°C. That’s far higher than the promise made under the Paris Agreement to keep heating to “well below 2°C”.

The bottom line is that the Paris Agreement will only be met if countries across the world rapidly reduce greenhouse gas emissions to zero, starting NOW. Yet this is NOT what is happening. See section on what global governments are ‘supposed’ to be doing to address the crisis.

The diagram below shows the future possible scenarios of global carbon dioxide emissions, along with what temperature the world will heat to by the end of the century if we follow each of these ‘emissions pathways’. However, it is important to be aware that the range of possible heating is actually wider than shown here. Crucially, this means that even with all the government’s current pledges in place we could be seeing over 4°C of heating by the end of the century. The diagram clearly shows that if we want to limit heating to 1.5°C we need to rapidly reduce emissions NOW.

Recently, the results of some new climate models caused great alarm because they indicated that we could be headed for even higher temperatures than earlier models had predicted. However, further studies showed that almost all of the additional heating predicted by the new models was due to cloud feedback loops, and such feedback loops are notoriously difficult to model (see section on cloud feedback loops). Indeed, whilst the new climate models did appear to be better than previous models at simulating cloud feedback loops in some respects, they were worse in others. Thankfully, more recent work has now shown that the hottest, worst-case scenario predictions of these new models are, in fact, unrealistic and that the models overestimate recent warming trends. Sadly though, the cooler, best case scenario predictions of these new models have now been ruled out too.

What remains clear is that we are most certainly headed for very dangerous levels of warming unless we urgently stop greenhouse gas emissions NOW.

The additional risks of feedback loops

Our Earth’s climate system is a complex web of interconnected systems that are not yet fully understood. As the atmosphere and oceans heat up, these different systems interact with each other, risking setting off “feedback loops”.

There are two types of feedback loops. Negative feedback loops occur when the Earth responds to warmer temperatures in ways that suppress the initial warming, bringing temperatures back down – thus stabilising the climate. In contrast, positive feedback loops occur when the Earth responds to warmer temperatures in ways that amplify the initial warming. In other words, warming leads to more warming, which leads to even more warming. Crucially, these kinds of feedback loops destabilise the climate and are therefore a major cause for concern. However, it should be noted that, in most cases, positive feedback loops do not lead to a “runaway” scenario – where the climate just keeps on heating up more and more – because on each cycle of the loop the feedback process causes less warming.

Throughout most of Earth’s history, negative feedback loops have tended to dominate, ensuring that the climate stays within a range of temperatures suitable for life. However, in our prehistoric past there have been times when positive feedback loops have taken over, amplifying large changes in the world’s climate such as the transitions from warm periods into ice ages.

Today we are playing a dangerous experiment with the climate, adding greenhouse gases into the atmosphere at unprecedented rates. As the atmosphere and oceans heat up, positive feedback loops could kick in at any time, sending warming shooting up even faster than it already is.

Today’s improved climate models incorporate many such feedback loops. It is therefore not correct to say that climate models do not take into account feedback loops. However, no climate model is perfect and there is always the risk of missing something important – which is why climate scientists also take detailed measurements of the planet and study past climates to provide real-world checks.

What this means is that it is virtually impossible to predict exactly how much heating we will see in response to different future carbon dioxide ‘emissions pathways’ (see graph in section on how hot it is likely to get and when). This leaves us with a big risk that, even if we do manage to reduce carbon dioxide emissions enough to – in theory – prevent really dangerous warming, the Earth’s atmosphere could end up heating up far more than most models predicted, due to feedback loops being more powerful than expected. This is why, if we want the best possible chance of keeping to the Paris Agreement and preventing catastrophic damage to our planet, it is even more crucial that we reduce carbon dioxide emissions as fast as possible.

Below are a few examples of feedback loops:

Water vapour and clouds

As temperatures go up, more water evaporates into the air. Water vapour is itself a greenhouse gas, meaning as more water evaporates the greenhouse effect gets stronger, causing more warming – a classic example of a positive feedback loop. The ‘water vapour feedback loop’ is one of the most powerful feedback loops, almost doubling the heating effect of increased carbon dioxide levels by themselves.

In addition, as the atmosphere gets more moist we also get more clouds. Not only does this increase the amount of rainfall, leading to bigger storms and dangerous flooding, clouds themselves also feedback on the climate. They do this in two opposing ways: clouds can cool the Earth by reflecting sunlight away from it, and they can warm it by trapping heat and stopping it from escaping out to space. This is why a cloudy day is cooler than a sunny day (more sunlight is reflected away), but an overcast night is warmer than a clear night (more heat is trapped). Hence clouds can result in both positive and negative feedback loops, at the same time. Which of these processes dominates depends not only on the total amount of cloud cover, but also on the types of cloud present and where and when they form. This makes cloud feedbacks notoriously difficult to model.

The ice-albedo effect

Due to its bright white colour (or high albedo), sea ice in the Arctic reflects most of the light and heat from the Sun back out to space. However, as the atmosphere warms, sea ice melts. If enough ice melts, the light-coloured reflective surface of the ice eventually disappears, exposing the darker surface of the ocean. This darker surface then absorbs the Sun’s rays rather than reflecting them, which makes the ocean heat up – a bit like how wearing a black shirt on a hot day makes you feel warmer than wearing a white one. As a result of increasing ocean temperatures, more sea ice melts, which in turn leads to the exposure of more dark water surface, which absorbs more heat, which melts more ice, and so on and so on.

The ice-albedo positive feedback loop

This ice-albedo positive feedback loop is a key reason why the Arctic is warming faster than anywhere else (known as Arctic amplification). Indeed, Arctic amplification has been linked to the drastic reduction in Arctic sea ice. To make matters worse, some climate scientists are now concerned that the amplification of warming in the Arctic is disrupting the Northern Hemisphere jet-stream, causing more extreme weather in the mid-latitudes – areas such as northern Germany, Poland, southern parts of the United Kingdom and the mid United States.

Melting permafrost

Permafrost is a type of soil that has been permanently frozen for many thousands of years. Globally it covers a whopping 15 million square kilometers, about a quarter of the Northern Hemisphere, mostly in Canada, Russia and Alaska. Permafrost is a huge store of carbon. Frozen Arctic soil, for example, holds an estimated 1,460 to 1,600 billion tons of trapped carbon – that’s almost twice as much carbon as is currently in the atmosphere. As permafrost melts, bacteria in the soil release vast quantities of this carbon back into the atmosphere in the form of methane or carbon dioxide. Methane is a powerful greenhouse gas with a warming effect many times that of carbon dioxide over short time scales. This causes more warming, which melts more permafrost, and so on.

Although the latest studies suggest that there is as yet “no evidence to date for increasing methane release from the Arctic” and only 5-15% of the trapped carbon is expected to be released this century – much less than could be emitted from fossil fuels – unprecedented heating in the Arctic is causing soils that have been permanently frozen for thousands of years to melt at faster and faster rates. If the permafrost melt rate keeps accelerating, the methane released would have terrible impacts on the climate. Even at slower rates of melting, the longer-term impact of the carbon dioxide released from melting permafrost is a serious cause for concern. If we can limit global heating to 1.5°C (as opposed to 2°C) we would prevent the thawing of approximately 2 million square kilometers of permafrost.

Wetland methane production

When plants at the bottom of rivers and lakes die, bacteria break them down, releasing methane. Warmer temperatures lead to the growth of more aquatic plants, leading to more methane production. This in turn causes more warming, leading to more plant growth, and so on. This effect is exacerbated by the loss of trees surrounding the lakes as a result of warming temperatures, as the debris from these trees would usually reduce methane production in the lake.

Wetlands are responsible for about half of all natural methane emissions – this is more than the methane emissions from oil and gas, almost as much as the methane emissions from cow burps and many times more than the emissions from melting permafrosts.

Methane levels in the atmosphere stopped rising in the early 2000s for the first time in hundreds of years, but then started increasing again after 2007 and then began accelerating rapidly in 2014. It is still a matter of debate exactly what is the cause of this recent rise, but an increase in methane emissions from tropical wetlands is one of the strongest contenders.

Drying soils and mega-heatwaves

Soils contain huge amounts of stored carbon. Warmer temperatures cause soils to dry out and release their carbon back into the air. This results in more warming, leading to even more soil drying and more carbon being released, and so on. Soils in the tropics store one third of all the carbon on land, and recent experiments show they are more vulnerable to heating than previously thought.

In addition, dry soils can’t absorb as much heat as moist soils. So as the atmosphere warms and soils dry out, more heat is radiated back into the atmosphere, leading to more drying resulting in even more heating. It is this kind of positive feedback loop that can trigger ‘mega-heatwave’ events.

Carbon cycle feedbacks

Trees and other plants absorb carbon from the air through photosynthesis and store it in wood and in the soil. Carbon dioxide is also removed from the air by the oceans. Collectively, these stabilising “carbon cycle feedbacks” absorb around 50% of the total human-caused carbon emissions, shielding us from the full effect our emissions would otherwise have had. However, it is possible that in the future something could happen to disrupt these processes, in which case we may find that our emissions start to cause even more warming than had previously been thought.

For example, warmer temperatures can lead to dryer forests and dryer soils, and this leads to more wildfires. These wildfires release carbon dioxide back into the atmosphere, which leads to more heating – which in turn causes more drying and more fires.

In addition, whilst plants tend to grow faster at higher levels of carbon dioxide (due to faster rates of photosynthesis), above certain temperatures further increases in photosynthesis can become impossible due to increasing heat stress. As a result, in hotter conditions some plants can simply stop growing – a phenomenon that can be easily observed in a vegetable garden, when, during the hottest period of summer, plant growth temporarily stops. And of course, when plants stop growing, they stop absorbing carbon dioxide. Recent research shows that some tropical forests could have already peaked in their absorption of carbon in the 1990s.

The bottom line is that if there is a reduction in the amount of carbon dioxide our trees, plants and soils absorb on a global scale, our carbon emissions budgets shrink accordingly, meaning that we would have to reduce emissions even faster than we currently need to, if we want to stay below 1.5°C heating.

How tipping points might make things even worse…

“Tipping points are so dangerous because if you pass them, the climate is out of humanity’s control: if an ice sheet disintegrates and starts to slide into the ocean there’s nothing we can do about that.”

Professor James Hansen, former Director of the NASA Goddard Institute for Space Studies

To make matters even worse, some feedback loops involve ‘tipping points’. A tipping point is a threshold above which a small change in temperature will cause the feedback loop to become self reinforcing. This would then push that part of the Earth’s system into an abrupt or irreversible change, resulting in a completely new state. It may take hundreds or even thousands of years for the change to play out fully once the threshold is crossed, but the worrying thing is that it would be practically impossible to reverse: the transition to the new state will then continue regardless of whether emissions subsequently go down. It’s like passing the point of no return as you approach a waterfall in your boat.

We don’t know with any certainty when these tipping points could occur, but the risk gets bigger with every fraction of a degree of heating. In other words, the higher our temperatures go, the greater the risk of passing a point of no return. Scientists have become increasingly concerned by the risk posed by tipping points at even relatively small increases in temperature. Indeed, recent research suggests that some tipping points are vulnerable to being passed even at (or indeed below) 2°C of heating.

Not all tipping points would cause further warming. Some might result in the collapse of an ecosystem (in response to the imminent wiping out of tropical coral reefs), or might result in more sea level rise (in response to the collapse of parts of the West Antarctic Ice Sheet. However, the point is that all tipping points all have the potential to cause catastrophic damage that is irreversible in our lifetimes. Indeed, the authors of a recent Nature paper warn that the danger posed by tipping points alone suggests we are in a state of planetary emergency: both the risk and urgency of the situation are acute.

There are a number of tipping points that we know about and should be extremely concerned about, and possibly more that we do not. Below, we describe a few of the key ones. To find out more, see this video where a group of us from the Extinction Rebellion Scientists community discuss tipping points with some of the leading scientists in the field.

Permafrost collapse

One important tipping point relates to the thawing of the Siberian permafrost. This will release both carbon dioxide and the more potent, but less long-lived, greenhouse gas methane. This increases heating, leading to more permafrost thaw, and so on (see section on the additional risks of feedback loops). Beyond a certain level of heating, probably around 3°C or more, we could see a wide scale collapse of the Arctic permafrosts. It is feared that the Arctic may have already crossed a key threshold.

Methane release from melting permafrost is often associated with the fear that warming oceans and melting of ice could release large amounts of methane now contained within ocean sediments. Thankfully, current research indicates that most of this methane will reach the atmosphere as the much less potent greenhouse gas carbon dioxide, which would mean we can breathe a sigh of relief. However, even if only small amounts of methane reach the atmosphere, or they reach it as carbon dioxide, the process remains a possible positive climate feedback or tipping point, and much more research and observations are needed to fully understand the level of risk.

To make matters worse, a worrying recent study has revealed that a process called “abrupt thaw” – involving rapid warming of small patches of frozen ground containing large veins of ice – will lead to the release of far more emissions from permafrost than once thought. Although less than 20% of northern permafrost is susceptible to this kind of rapid thawing, the researchers warn that this process is likely to double the overall contribution of permafrost to the warming of the planet.

As Merritt Turetsky, director of the Institute of Arctic and Alpine Research (INSTAAR) at CU Boulder, explained: “Forests can become lakes in the course of a month, landslides occur with no warning, and invisible methane-seep holes can swallow snowmobiles whole.”

Ice sheet slippage

“This finding should be of huge concern for all those who will be affected by sea level rise. If this very high rate of ice loss continues, it is possible that new tipping points may be breached sooner than we previously thought.”

Dr. Louise Sime, Climate Scientist at the British Antarctic Survey

“Nobody expected the ice sheet to lose so much mass so quickly, things are happening a lot faster than we expected.”

Isabella Velicogna of the University of California, Irvine

Ice sheets on land, such as glaciers and the continent-size ice sheets in Greenland and Antarctica, may give rise to another feedback loop. As the ice melts, water percolates into the ground below it, making the rock slippery, which could make it easier for layers of ice to slide over the bedrock they sit on, accelerating the collapse of glaciers into the surrounding sea.

In addition, warming ocean waters make ice shelves vulnerable to melting. Ice shelves protect ice sheets and stop them from slipping down the bedrock and into the sea. Once ice shelves start melting, an irreversible process can be set in motion which leads to the disintegration of entire ice sheets. The problem is, because ice sheets sit on land, when they collapse they lead directly to sea level rise.

Worryingly, the last time carbon dioxide levels were as high as they are today – during periods of the Pliocene era around 3 million years ago, when global temperatures were around 2-3°C higher – sea levels were a whopping 20 m higher than today. Most of this sea level rise was due to the melting of ice sheets ‘grounded’ below sea level and therefore extremely vulnerable to warming seas. These included most of the current West Antarctic Ice Sheet and parts of the East Antarctic Ice Sheet.

Indeed, during the warm period that preceded the last ice age around 125,000 years ago, warming seas were the major driver for the collapse of all or parts of the West Antarctic Ice Sheet. This collapse has been linked to a rapid and irreversible recession of the grounding line – the boundary between the grounded glacier and where it becomes a floating ice shelf.

Given that our current temperatures are similar to those of the last interglacial warm period, and our carbon dioxide levels considerably higher, this leaves us with the terrifying possibility that even current levels of heating are enough to tip over the West Antarctic Ice Sheet, which could lead to increased sea level rises for centuries to come, even if we stop emitting greenhouse gases. Worryingly, recent observations suggest this process could already be underway, although it is not clear quite how much this sea level rise this would cause this century. What’s equally concerning is that unexpected melting is underway in the East Antarctic, an area that is usually seen as being pretty stable.

Thermohaline circulation

Another important tipping point relates to ocean circulation, which plays a crucial role in maintaining regional climates. As Arctic sea ice and the Greenland ice sheet melt, it is feared that changes in ocean circulation in the Atlantic may divert the Gulf Stream. The Atlantic Meridional Overturning Circulation (AMOC), a large system of ocean currents that carry warm water from the tropics northwards into the North Atlantic, has already weakened by about 15% since the middle of the 20th century. If there is continued decline, it would significantly change regional weather patterns and could lead to a significant cooling in Western Europe, even as the rest of the world as a whole heats up, causing massive disruption.

Forest dieback

Trees usually absorb water from the soil and release it back into the atmosphere as evaporation from their leaves. Large forests, such as the Amazon, are self-sustaining in this way, evaporating the water they need in order to survive. Fewer trees means less water can be released from leaves therefore the atmosphere becomes even dryer. Once a certain amount of forest is lost, this can trigger a phenomenon known as dieback, in which the forest dries out entirely and transitions to a completely different ecosystem. To make matters worse, lack of water also weakens trees so that a bark beetle or other predator outbreak is more damaging. Once there are entry wounds in a tree, fungal spores (which are everywhere) can get in and rot the tree.

It is thought that most forests are not at risk of dieback until temperatures get above 3°C of heating. However, it could happen sooner than this due to increased deforestation. Indeed, scientists have warned that the Amazon may already be dangerously close to a tipping point and further deforestation could tip it over the edge, leading parts of the rainforest to dieback and transition to a savannah, releasing billions of tonnes of carbon in the process. (See section on deforestation).

The compound risk of multiple tipping points

Evidence is mounting that not only could the chance of crossing tipping points be higher than was previously thought, but that tipping points could also be interconnected across different biophysical systems. Indeed, it is feared that once a single climate process passes its tipping point, this could push other processes beyond their own tipping points, triggering other tipping points – and so on. This gives rise to the possibility of a tipping cascade, and with it, multiple disasters.

This article gives a more detailed explanation of nine key tipping points that could be triggered by climate change. They are represented more simply in the diagram below, which also shows at what temperature each tipping point is at risk of being breached and how they are all connected with each other:

Global map of potential tipping cascades. Individual tipping elements are colour-coded according to the estimated thresholds in global average surface temperatures that could trigger them to become tipping points. Arrows show potential interactions between tipping elements, based on expert knowledge, that could generate tipping cascades.

While it is unlikely that interacting feedback loops will cause “runaway” global heating, the longer we emit greenhouse gases and the hotter it gets, the more likely that multiple interacting tipping points could push the Earth into a much hotter state, known as a “Hothouse Earth”, from which it would be impossible to return for thousands of years. In other words, there could come a point where devastating changes to our world get locked in by processes that have escaped our control.

There has been a lot of misinformation spread about the “Hothouse Earth” hypothesis. It is important to be aware that it has not yet been proven for certain and, even if it is true, it may take hundreds or even thousands of years to play out.

However, even though the most extreme impacts of tipping points may take a long time to come to pass, the existential risk posed by the possibility of crossing multiple tipping points if we go above certain – unknown – temperature thresholds is very real. Indeed, the idea that human activity can completely transform the planet for thousands of years to come is profound. This really hammers home the need to reduce emissions to zero NOW, and to limit heating to less than 1.5°C.

It’s also worth being aware that even if a tipping cascade does get underway, it would still be worthwhile reducing emissions as quickly as possible, as this would slow the rate of change, buying societies and ecosystems some time to adapt and giving us a chance to limit damage and reduce suffering.

What will our world look like in 2050 if we don’t take radical action now?

“The climate emergency is our third world war. Our lives and civilization as we know it are at stake, just as they were in the second world war.”

Professor Joseph Stiglitz, Economist

With our governments not doing nearly enough to keep to the Paris Agreement (see section on what global governments are ‘supposed’ to be doing to address the climate crisis), and with the risks of triggering more feedback loops and breaching tipping points getting ever greater by the day, it certainly looks like it’s going to get a lot hotter. But just what will the future bring? How will it affect our lives? And do we really need to be worried about just a few more degrees of heating? In a word, yes.

On our current pathway, even with all the fully implemented government policies in place, we are likely to hit 1.5°C of heating by around 2030 and 2°C by 2050, or perhaps even sooner (see section on how hot it is likely to get and when).

If we allow this to happen, by 2050 our world will be utterly transformed from the one we grew up in, as we shall see in the sections below. However, it’s important to be aware that these temperature ‘milestones’ are not hard limits. Even 1.5°C of warming carries enormous risks, it’s just that this is the best we can hope for given what we have already emitted. Similarly, we won’t be catapulted into catastrophe as soon as we pass 2°C of heating. The changes our planet faces are on a sliding scale, with increasingly greater risks of more disastrous impacts with each fraction of a degree.

2050: More intense heatwaves and forest fires

“We will start to see the extreme end of the fire behaviour scale occur more frequently because of the increase of temperatures.”

Dr Richard Thornton chief executive of the Bushfires & Natural Hazards Cooperative Research Centre

By 2050 we expect to see around 2°C of average global heating, but some regions will heat up by a lot more than that. This means that the chances of there being extreme hot weather events across the globe will increase massively.

Graph showing how increases in the mean (average) global temperature affect the probability of extreme hot weather events occurring

Even by 2040, it is predicted that extreme heat waves – such as the one in 2003, when approximately 70,000 more people died than in a usual year, that led to over $15 billion in economic losses – will become an average European summer. In fact, by 2060, almost all summers will be hotter than that.

The IPCC warns that at a global average of 2°C heating we will be experiencing extreme heat waves of the kind seen in 2019 every summer. The deadly heatwaves that India and Pakistan saw in 2015, which killed over 3,400 people, may also occur annually. Compared to a heating of 1.5°C, an additional 350 million people across the globe will be at risk of heat stress, an additional 420 million people will frequently be exposed to extreme heatwaves, and an additional 65 million people will be exposed to exceptional heatwaves. Under even a relatively optimistic carbon emissions scenario, it is predicted that 22% of major cities will be heated to the point that their climate is unlike any currently existing city.

Extreme heat will cause misery for those who are unable to afford air conditioning, with workplaces becoming unbearably hot – leading to loss of economic productivity and exacerbating existing inequality. In addition, many countries are simply not equipped to deal with such periods of intense and prolonged heat and critical infrastructure (such as transport systems) will not be able to cope.

The UK Met Office warns that British summers are going to keep getting hotter, on average 3°C warmer and 18% drier. By 2050, the UK is predicted to see a trebling of heat-related deaths – with 7,000 dying due to excess heat each year – and the climate of Leeds is predicted to become more similar to that of Melbourne, with scorching summer heat waves like in 2018 every other year. These are conditions that no UK infrastructure is designed to withstand, nor that any of the wildlife and ecosystems of Northern England are adapted to.

2050: More intense storms, floods and hurricanes

Over the coming years, the likelihood of extreme rainfall events is expected to grow more than fourfold in some regions, with much of the world, including Europe and the UK, very likely to feel the catastrophic impacts of more frequent severe storms, stronger hurricanes, and more devastating floods. The UK Met Office warns that British winters will get wetter, with extreme flooding events becoming increasingly common. The intensity of rainfall during British summers is expected to increase too, suggesting that, whilst summers may tend to become drier overall, when it does rain it will fall in heavier bursts, with major implications for flash flooding.

The IPCC predicts that by 2050 the combination of rising seas and more intense storms will mean that, in many low-lying megacities and small islands, the sort of extreme flooding events previously occurring only once a century could be happening every year.

By 2050 we can also expect to see an increase in the amount of rainfall accompanying tropical cyclones, with an increase in tropical cyclone intensity and an increase in the number of very intense (category 4 and 5) tropical cyclones. It is predicted that tropical cyclones are more likely to be hitting Western Europe.

2050: Increased droughts and water shortages

“We know that with increased storms, increased floods, droughts and heat waves, production of food will be more problematic. Ensuring people have access to clean, safe drinking water will become much more difficult.”

Professor Mark Maslin, Professor of Climatology at University College London

“On the present projections, many parts of our country will face significant water deficits by 2050, particularly in the southeast, where much of the UK population lives.”

Sir James Bevan, chief executive of England’s Environment Agency

An estimated 3.6 billion people (nearly half the global population) already live in areas that are potentially water-scarce at least one month per year. The UN warns that, by 2050, between 4.8 billion and 5.7 billion people will be living in areas that are water-scarce for at least one month each year. Indeed, according to UN-endorsed projections, by 2030, due a combination of climate change, human action and population growth, global demand for fresh water will exceed supply by a staggering 40%.

By around 2050 the IPCC warns that 410 million people living in urban areas will be regularly exposed to severe drought, 50% more people may see increased climate-induced water stress, and 184-270 million more people will be exposed to increases in water scarcity.

It’s not just droughts and population rises that can cause water scarcity. 78 of the world’s mountain ‘water towers’ (reservoirs of freshwater locked away in high altitude snow, glaciers and mountain lakes) are incredibly vulnerable to the effects of global warming and climate change. Indeed, melting mountain glaciers threaten to put the 1.9 billion people living downstream of them at risk of serious water shortages for drinking water and crop irrigation. That’s more than one fifth of the world’s population.

In the Andes and the Himalayas alone, the melting of glaciers threatens the water supplies of hundreds of millions of people, leading to a potential reduction in water supply for more than 240 million people. The Indus river basin (stretching from the Himalayan mountains in the north to the plains of Pakistan in the south and finally flowing out into the Arabian Sea) is globally the most important such water tower and it is highly vulnerable to climate change. This water tower currently supports 206 million people. However water supplies are set to decrease in line with warming air temperatures while the population is set to increase. Glaciers are also important for hydropower and irrigation, so glacier melting will also put electricity and food supplies at risk.

In Europe, the loss of these frozen water towers will have a devastating impact on mountain regions important for providing water to France, Germany, Spain, such as the Rhone in France and the Rhine in Germany, as well as the Bulgarian Black Sea Coast and the Caspian Sea Coast. The Rhine region relies on water for power and industry too.

According to Dr Bethan Davies, from the Department of Geography at Royal Holloway University: “Limiting global warming to 1.5°C relative to pre-industrial temperatures will retain around 75% of all mountain glaciers, which provide a critical buffering service in the world’s mountains.”

It’s not just mountainous regions that will be at risk of water shortages. London is listed in the top 10 most likely cities in the world to hit Day Zero – the name given to the day when a city completely runs out of fresh water. According to the Greater London Authority, the city is likely to have supply problems by 2025 and “serious shortages” by 2040. In March 2019, Sir James Bevan, chief executive of the Environment Agency, warned: “On the present projections, many parts of our country will face significant water deficits by 2050, particularly in the southeast, where much of the UK population lives.” He explained that in about 20-25 years, demand for water could close in on supply, in what he described as “the jaws of death – the point at which, unless we take action to change things, we will not have enough water to supply our needs.”

2050: Rising seas and increased coastal flooding

“The future for low-lying coastal communities looks extremely bleak… But the consequences will be felt by all of us. There is plenty to be concerned about for the future of humanity and social order”

Prof Jonathan Bamber at Bristol University

As global temperatures continue to rise, we risk triggering the collapse of more sectors of the West Antarctic ice-sheets. Indeed, global heating of 1.5-2°C may well lead to collapse of the major Antarctic ice shelves, locking in a long-term and unstoppable sea level rise of several metres over the next few centuries – possibly sooner if temperatures continue to increase. Even if we are able to limit global heating to 1.5°C, sea levels still are predicted to continue to rise for hundreds of years – every 5 years we delay action locks in another 0.2 m.

Unless we drastically reduce emissions now, the IPCC predicts that, by 2050, the combination of rising seas and more intense storms will mean that, in many low-lying megacities and small islands, the sort of extreme flooding events previously occurring only once a century could be happening every year. Indeed, new studies show that if we don’t adapt and build sea defences, land currently inhabited by more than 300 million people is likely to flood at least once a year – that’s three times more than was previously thought. Rising sea levels are predicted to overwhelm the ability to build adequate coastal defences, forcing many millions of people to have to leave their homes.

See here for an interactive map showing which areas of the globe are predicted to be below annual flood level by 2050. Large parts of Vietnam, the world’s third largest rice exporter, could practically disappear, with almost 25% of the Vietnamese population – that’s more than 20 million people – living on land that is likely to be underwater at least once a year. 10% of people in Thailand also live in areas like this. Basra, Iraq’s second-largest city, could practically disappear too, triggering local conflicts. Other cities most at risk from sea level rise include Kolkata, Mumbai, Ho Chi Minh City, Shanghai, Bangkok and Miami. Without major investment, flooding in cities across the globe is forecast to cost over US$1 trillion per year.

Colette Pichon Battle, Executive Director of the Gulf Coast Centre for Law and Policy, warned: “The impact on families [of rising sea levels] is going to be something that I don’t think we could ever prepare for.”

The UK will be one of the worst hit, with large parts of the English coastline and areas around its rivers, such as Sussex, Kent, Cambridgeshire and Central London, predicted to regularly fall below sea level by 2050. Although it’s worth being aware that experts in Cambridgeshire have responded to these flooding projections with promises of an “ongoing commitment from all organisations to maintaining and improving flood defences already present in Cambridge and the Fens”. Even so, the Environment Agency estimates that 800 coastal homes in the UK will be lost in the next 15 years and that rising seas are likely to eventually force many people to have to relocate.

The residents of sea-threatened Fairbourne in Wales could be the first entire UK community in which rising sea levels and eroding coastlines will force people to have to relocate. Sea defences in this area will stop being maintained in the 2050s, but the local council says it may begin “decommissioning” the village before then and start moving residents out, potentially creating hundreds of British climate refugees.

2050: More devastating loss of wildlife on land and in the oceans

“Climate change is the biggest threat wildlife will face this century”

National Wildlife Federation

“The climate crisis has arrived and is accelerating faster than most scientists expected. It is more severe than anticipated, threatening natural ecosystems and the fate of humanity.”

World Scientists’ Warning of a Climate Emergency

Over the next decades, without radical intervention, wildlife will continue to decline with an estimated one million species facing extinction due to human action.

We have already locked in a large future increase in marine heatwaves due to the fact that our oceans respond very slowly to atmospheric heating. Indeed, the IPCC warns that marine heatwaves are projected to further increase in frequency, duration, spatial extent and intensity. This will have devastating impacts on ocean life.

The latest studies suggest that the Arctic could be ice-free in summer as soon as 2035, with devastating impacts on polar bear populations and other Arctic ecosystems. By 2050, more than 99% of our tropical coral reefs will have been lost: that is near total destruction of some of the most important and diverse ecosystems on the planet, which support up to one million other species and provide food, protection from storms and livelihoods for nearly one billion people.

Losing the diversity of our ecosystems, combined with climate breakdown, will place huge strains upon our social systems. It is feared that this could ultimately result in the collapse of our globally interconnected network of civilizations, resulting in great suffering and the deaths of many hundreds of millions, and perhaps even billions, of people.

2050: Further reductions in food production

“Climate change will lead to battles for food.”

Jim Yong Kim, Former President of The World Bank

At even 1.5°C of heating, predicted to happen around 2030, in West Africa and the Sahel reduced maize and sorghum production is likely, with the size of areas suitable for maize production reduced by as much as 40%, leading to increased risks of undernutrition.

At 2°C of heating, expected by around 2050 unless we make radical changes, the risk of extreme weather hitting several major food producing regions of the world at the same time could more than triple. Land degradation and climate change together are predicted to reduce crop yields by an average of 10% globally and up to 50% in certain regions. U.S. maize production could decrease by about 18%, and there is predicted to be a roughly 7% risk of the world’s top four maize exporters suffering simultaneous crop failures of 10% or more. Rice and wheat will become less nutritious, and there will be a higher risk of malnutrition. Continued loss of pollinating insects would affect more than 75% of global food crop types, reducing yields and risking US$235-577 billion of global crop output annually.

Infographic showing the vulnerability of non-OECD countries to the threat of food insecurity due to climate change by 2050 if we fail to reduce emissions or adapt to changes

Overall, by 2050, up to 1.5 billion MORE people (that would be five billion people in total) particularly in Africa and South Asia, are likely to face shortages of food and clean water.

In the absence of good governance, food insecurity in some parts of the world, resulting in a domino effect of price hikes across the globe, could lead to a dramatic increase in the incidence of food riots.

The UK, for example, is dependent on a complex global industrial consumer economy. Around 50% of UK food comes from foreign imports, including about 70-80% of fruit and vegetables. Some reports even suggest that, if we include the imported ingredients in products that are processed in the UK, up to 80% of all our food relies on foreign imports. Imports are mainly from mainland Europe, where crops are already susceptible to damaging heatwaves. The UK Climate Change Risk Assessment highlighted food security issues from both domestic and international supply chains as a key risk in need of urgent action.

To make matters worse, a new study has shown that, when compared against the real world impacts of the 2003 European heatwave, even ‘state of the art’ models of the impacts of climate breakdown still underestimate the scale of the impacts of heatwaves on important sectors such as agriculture. The authors state that this “means that societal risks from future extreme events may be greater than previously thought”.

2050: More devastating impacts on human health

“Climate change poses the biggest global health threat of the 21st century”

The Lancet Commision on Climate Change

Warmer temperatures will continue to increase the spread of infectious diseases such as malaria and dengue fever, with risks of them appearing in new parts of the world.

According to the World Health Organisation (WHO), between 2030 and 2050, climate change is expected to cause approximately 250,000 additional deaths per year, from malnutrition, malaria, diarrhoea and heat stress alone.

The WHO has identified malaria as one of the most climate-sensitive diseases and predicts at least another 60,000 deaths from it by 2050. Countries that have eradicated the disease could see a deadly return – including parts of Europe. Increasing numbers of new diseases and viruses may also appear by 2050. Allergies are predicted to be much worse by 2040 too – with about 2.5 times as many grains of pollen per cubic metre of air as there is today. See section on more intense heatwaves for information on how heat-stress – and the numbers of heat-related deaths – is predicted to increase by 2050.

According to a new report from the Organisation for Economic Co-operation and Development (OECD), by 2060, unless action is taken, outdoor air pollution alone could cause 6 to 9 million premature deaths a year and cost 1% of global GDP – around USD 2.6 trillion annually – as a result of sick days, medical bills and reduced agricultural output.

2050: Mass displacement

“Climate change is the result of the greatest market failure the world has seen. We risk damages on a scale larger than the two world wars of the last century. What we are talking about is extended world war. People would move on a massive scale. Hundreds of millions, probably billions of people would have to move.”

Lord Nicholas Stern, Professor of Economics and Government

New studies show that by 2050, sea-level rise will result in annual flooding of land currently home to 300 million people (three times more than was previously thought), overwhelming the ability to build adequate coastal defences and forcing many millions of people to have to leave their homes. This will particularly affect parts of Asia, with cities in China, Bangladesh and India having the greatest numbers of people at risk.

The World Bank has estimated that by 2050 there could be 140 million people in Sub-Saharan Africa, Latin America and South Asia who will be forced to move within their countries due to climate change – as a result of high temperatures, crop failures and flooding. These refugees will be moving out of harm’s way as migration is essentially a form of adaptation to a more hostile world. According to a study carried out by the Institute for Environment and Human Security of the United Nations University, by 2050 there could be up to 200 million environmental migrants globally, with most displacement occurring within nations or to bordering countries.

2050: Poverty and financial instability

“Once climate change becomes a defining issue for financial stability, it may already be too late.”

Mark Carney, former Governor of the Bank of England

Compared to an average global heating of 1.5°C, at 2°C heating the IPCC warns that an additional several hundred million people will be left susceptible to the risks of climate-related poverty. Between 3-16 million people could be forced into extreme poverty because of rising food prices and crop failures.

In terms of the global economy, climate change is set to have a myriad of negative impacts, and indeed there may be many financial benefits from measures undertaken to tackle climate change, as summarised in this article. The IPCC predicts that, in the United States alone, each degree of warming will lead to a loss of 2.3% of GDP. On our current trajectories, by 2050 this will amount to financial losses in the US of more than $446 billion. However, the economic models the IPCC use to make these predictions have come under criticism by many economists and climate scientists, and actual losses are likely to be much higher.

2050: Social instability and conflict

“The political and economic map of the world simply cannot cope with these stresses, without real change in the way nations plan, govern and commit resources. Disaster relief will likely be inadequate, insurance funds will probably fail, and vast dislocations of supplies and services are to be expected. Having a capable army and rescue services will not be enough. The threat of mass casualties, political upheaval, and conflict within and between states will certainly increase”

General Wesley K Clark (Ret.), Former NATO supreme allied commander for Europe

There are concerns that mass migration caused by rising seas or agricultural failure could trigger or exacerbate regional conflicts – especially in some countries such as Iraq, whose second largest city Basra is predicted to be almost totally submerged by 2050 – driving political instability and increasing the chances of armed conflict and terrorism. General Castellaw, a member of the advisory board of the Centre for Climate and Security, told the New York Times: “So [rising sea levels] is far more than an environmental problem. It’s a humanitarian, security and possibly military problem too.”

What will our world look like by the end of the century?

“The next 20 years will be worse than the last 20 years – all indications point to that – and things will be completely nuts by the end of the century if we keep doing what we’re doing now.”

Dr Angeline Pendergrass, National Center for Atmospheric Research (NCAR) in Boulder, Colorado.

Taking into account climate policies that were in place in December 2019 we are heading towards an average global temperature rise of 3°C by the end of the century, with a significant chance that we could be hitting 4°C heating or more.

2100: extreme weather

At 3°C of heating, where we are currently most likely to be headed for by the end of the century, the increase in extreme weather events will be devastating. Drastic increases in heatwave duration and frequency will lead to substantial impacts on human health, mortality and the global economy. There will be large reductions in rainfall and water availability resulting in large increases in extreme drought and very high risks of water deficit. Scientists predict that by 2100 the intensity of tropical storms in the Western North Pacific could increase substantially.

Changes in average typhoon intensity in the Western North Pacific from 1950 to present day and predicted increases in typhoon intensity up to 2100.

2100: flooding and mass migration

The IPCC predicts that by 2100, the combination of rising seas and more intense storms will mean that, in most areas, the sort of extreme flooding events previously occurring only once a century could be happening every year. Huge areas of land across the globe could become uninhabitable and we are likely to see a huge increase in mass displacement and climate refugees.

2100: wildlife loss

Without urgent action, over the next century the combination of rapid changes in the climate and human-caused damage to our land will lead land-based ecosystems to be faced with an environment that will be unlike anything seen in our recent evolutionary history. It is predicted that 640,000 more species will be at risk of extinction – in addition to the one million species already threatened with extinction over the coming decades due to human action (see section on how we are destroying our wildlife).

The changes in our environment will not only be of a similar magnitude to the very largest changes that have taken place in the last 65 million years, but they will also be happening many times faster. To make matters worse, while in the past creatures could have migrated to cooler areas to seek refuge from rising temperatures, many such areas have now been severely degraded, fragmented or colonised by human activities. In addition, the speed of the changes that will be taking place means that many plants and animals will not be able to migrate fast enough to keep up with climate change, even if there were to be the habitats to move to.

It is very likely that by the end of the century, unless we make radical changes now, we will see drastic warming at the poles, with the Arctic very likely to be ice-free each summer – leading to critical habitat losses for organisms such as polar bears, whales, seals, and sea birds. A collapse in permafrost may occur. Alpine habitats are also likely to suffer critical losses and we are likely to see increases in the frequency of marine heatwaves of around 50 times, relative to pre-industrial times, with devastating impacts on ocean life.

2100: impacts on human health, food and water

By the end of the century human health will be drastically impacted by extreme weather events and heat stress. In addition, increasing temperatures will lead to a large increase in the spread of infectious diseases. For example, by 2061-80, an additional half a billion people could be at risk from diseases carried by the Aedes aegypti mosquito.

By 2100 there will be substantial reductions in agriculture and crop yield, resulting in major regional food insecurities and very high risks of under nutrition, especially in communities dependent on dryland agriculture and livestock. It is predicted that there will be a 10-30% decrease in overall crop production. Major droughts and crop losses in one part of the world will affect food prices on the other side of the world. More than 10 million tonnes of fish will be at risk every year, worth tens of billions of dollars.

In addition, IPCC projections state that most glaciers – the world’s largest supplies of mountainous freshwater – will be gone by 2100. Globally, about 1.9 billion people live downstream of glacierised mountain ranges and depend on the water from these glaciers for drinking water, irrigation and industry. In places like the Himalayas, glacier recession will lead to very severe water shortages.

Whilst 3°C warming would be terrible, there is a significant chance that we could reach a catastrophic 4°C warming by the end of the century…

What will our world look like by the end of the century if we reach 4°C of heating?

“There is a growing sense of panic in those who really understand what a 4°C world might be like.”

Professor Will Steffan, Director of the Australian National University Climate Change Institute

On our current emissions pathways there is a significant chance that temperatures could sail past 3°C of heating, reaching a terrifying 4°C (or more) of heating by the end of the century, made all the more likely if governments renege on their promises to cut emissions or if positive feedback loops kick in and tipping points are breached. In fact, if feedback loops are much stronger than we expect, 4°C of heating could be reached as early as the 2060s – under an extreme worst case scenario.

Professor Richard Betts, Chair of Climate Impacts at the University of Exeter and Head of Climate Impacts at the Met Office Hadley Centre, warns: “Global warming of 4°C this century is quite possible and would bring massive risks to life and society – heatwaves, coastal and river flooding, droughts and more… We don’t know how society would respond to the massive risks of 4°C global warming. Transformational change would be needed.”

Even if emissions slow down, until they reach net zero the world will keep heating up and we’ll reach 4°C heating sooner or later – a situation we simply cannot allow to happen.

Professor Kevin Anderson, deputy director of the Tyndall Centre for Climate Change Research, warns: “There is a widespread view that a 4°C future is incompatible with any reasonable characterisation of an organised, equitable and civilised global community.”

Professor Johan Rockström, director of The Potsdam Institute for Climate Impact Research, has said that in a 4°C-warmer world: “It’s difficult to see how we could accommodate 8 billion people or even half of that. There will be a rich minority of people who survive with modern lifestyles, no doubt, but it will be a turbulent, conflict-ridden world.” By 2100, in the absence of the catastrophic impacts of global heating, it is predicted that we would be heading for a population of around 11.2 billion.

According to a World Bank report in 2012: “…there is also no certainty that adaptation to a 4°C world is possible. A 4°C world is likely to be one in which communities, cities and countries would experience severe disruptions, damage, and dislocation, with many of these risks spread unequally. It is likely that the poor will suffer most and the global community could become more fractured, and unequal than today. The projected 4°C warming simply must not be allowed to occur.”

Here are a few more specific predictions about what a 4°C hotter world would look like:

4°C of heating: extreme heat

At 4°C of heating, up to three quarters of the world’s population could be at risk from deadly heat extremes, with billions facing a ‘deadly threshold’, as shown in the figure below adapted from the study.

Number of days per year exceeding the threshold of temperature and humidity beyond which climatic conditions become deadly. Top: average between 1995-2005 (historical); bottom: average between 2090-2100 in a world 4-5°C hotter than in preindustrial times

The combined increase in temperature and humidity could become so high in the densely populated agricultural regions of South Asia that towards the end of the century there could be days when humans will not be able to tolerate being outdoors for more than a few hours at a time. In North China, deadly heat waves may limit habitability of one of the world’s most populous regions in the world, leading to heat extremes that exceed “the threshold defining what Chinese farmers may tolerate while working outdoors.” Huge areas of the world will become uninhabitable. Even somewhere cool like the UK will have temperatures above 40°C every few years, much hotter than the current hottest day on record.

4°C of heating: rising seas, flooding and mass displacement

At 4°C of heating, we would expect to see a sea level rise of up to one metre (with much more locked in over the coming centuries), but, if emissions are high and there is a large contribution from melting ice sheets, there is more than a 10% chance of it exceeding two metres – quite possibly a lot more if parts of the West Antarctic Ice Sheet have collapsed by then. Land currently inhabited by 230 million people is predicted to be below the waterline at high tide – potentially resulting in daily flooding – with some island nations “likely to become uninhabitable”.

Given that the West Antarctic Ice Sheet is responding to climate change even more quickly than scientists first thought, it is possible that we could even be headed towards a rise of two metres by the end of the century – although other studies suggest it may not be quite as much as this. Sea level rise won’t stop in 2100 either. If warming is sustained we will be committed to around a 5m sea level rise over the coming centuries if the West Antarctic Ice Sheet collapses, and up to another 7 m if the Greenland ice sheet melts.

At 4°C of heating the Alps could become almost completely deglaciated. In Europe alone, an additional 250,000 to 400,000 people would be exposed to river flooding each year – and up to 5.5 million per year to coastal flooding – and annual coastal flood damages are projected to increase 100 to 1,000 times.

In the UK, The Environment Agency estimates that 7,000 properties around England and Wales, worth more than £1 billion, will be lost to rising seas over the next century as coastlines erode. They say that the cost of protecting these properties is considered to be too high. The Committee on Climate Change had previously warned that 1.2 million homes in England will be at significant risk from coastal flooding by 2080, though this number is likely to now be far higher.

Overall, global sea level rise is expected to displace hundreds of millions of people by 2100, and eventually rising seas are predicted to displace the 680 million people living in low-lying coastal zones, along with the 65 million citizens of small island states.

4°C of heating: wildlife loss

As the climate becomes radically different to what species have experienced previously or are able to adapt to, it is predicted that at 4°C heating about 1.3 million more species will be at risk of extinction (about 16% of all species) and 15% of species communities will suffer abrupt and disruptive changes. However, these numbers are likely to be too conservative as they are based on average changes in temperature and rainfall, and it is difficult to predict how many extra species will be driven extinct by additional processes such as extreme weather events, and local changes such as the melting of sea ice. It’s important to realise that these numbers are in addition to one million species currently at threat from due to over-exploitation of the land and sea by humans (see section on how we are destroying our wildlife).

At 4°C of heating, the additional carbon dioxide in the atmosphere is predicted to cause the acidity of the world’s oceans to rise by 150%. It is thought that, in our prehistoric past, extreme changes in ocean acidity like this played a large role in mass extinction events.

4°C of heating: reductions in food production

At 4°C of heating the production of maize in the US, much of which is used to feed livestock and make biofuel, could be cut in half. The risk of the world’s top four maize exporters suffering simultaneous crop failures of 10% or more shoots up to a terrifying 86%. Yields of global vegetables and legumes could fall by 35% due to water scarcity and increased salinity and ozone. Food shocks will be felt across the globe and, as a result, the risk of civil unrest, and even societal collapse, would be expected to increase dramatically.

According to Rachel Warren, Professor of Global Change and Environmental Biology at the University of East Anglia: “We have already observed impacts of climate change on agriculture. We have assessed the amount of climate change we can adapt to. There’s a lot we can’t adapt to even at 2ºC. At 4ºC the impacts are very high and we cannot adapt to them”.

Not worth the risk: why we need to apply the Precautionary Principle

“If you got in a plane with a one in 100 chance of crashing you would be appropriately scared. But we are experimenting with the climate in a way that throws up probabilities of very severe consequences of much more than that.”

Sir David King, Former UK Chief Scientist and Former UK Special Representative for Climate Change

Climate modelling is about making predictions about how likely it is that something terrible will happen in the future if we don’t take radical action now. It is impossible for science to tell us with absolute certainty what will happen, but we can say that certain things – such as more extreme weather, rising sea levels, crop failures and water scarcity – are “extremely likely” to happen. Other aspects, such as tipping points, are more uncertain, but if they do occur would cause catastrophic and irreversible damage. In other words, we can say that if we don’t act now, we risk global catastrophe, even if we can’t say exactly when it might occur.

However, some people say that if the impacts of climate change are not proven, no matter how bad they may be we shouldn’t risk potential economic harm by taking action. They say “come back to us when you’re certain”.

This is where we need to apply what’s known as the Precautionary Principle. The Precautionary Principle advises us that “when an activity raises threats of harm to human health or the environment, precautionary measures should be taken, even if some cause and effect relationships are not fully established scientifically.” In other words, if there’s a plausible risk that a certain activity may have environmentally harmful consequences, it is better to control that activity NOW rather than wait for incontrovertible scientific evidence that it will cause harm. We have seen people applying the Precautionary Principle in making significant changes to their lifestyles and their routine due to the risk of catching the COVID-19 coronavirus.

Yet the vast unknowable risks to which we are potentially exposed as a result of human-caused climate change and ecosystem breakdown are many orders of magnitude greater than those posed by coronavirus. Whilst they may be less immediate and tangible than the risks of catching coronavirus, these risks are incredibly serious and the consequences potentially devastating. It is therefore extremely unwise to wait until all the evidence is in before acting radically to head off such risks. In fact, by the time scientists are certain about exactly what will happen next, it will almost certainly be too late to stop it.

Rapidly reducing greenhouse gas emissions may indeed cause significant disruption to our lives and even possible economic harm. Yet not doing so risks catastrophic impacts on our planet, with incalculable suffering and the deaths of hundreds of millions, if not billions, of our fellow human beings. That could never be worth the risk. Nothing is worth risking everything for.