Further warming will put more people around the world at risk of an unprecedented catastrophe. Once net zero CO2 emissions are achieved, temperatures will soon stop climbing. This brings a glimmer of hope, but it also puts pressure on governments and major businesses
Text | Friedrich Otto
It's almost impossible not to notice that the weather in 2021 (on a global scale) is going to be bizarrely bad. Such a thing happened in China, where floods in Henan affected millions of people and killed more than 300 people, the same fatal flood a year earlier. North America was not spared, with a "heat wave dome" that raised temperatures in Canada to nearly 50 degrees Celsius, killing hundreds of people and causing wildfires to destroy entire towns. In Europe, this summer's floods washed away several regions in Germany, Belgium and neighboring countries, while fires from extreme heat erupted in the south. Meanwhile, floods in Nepal, Pakistan and Afghanistan claimed hundreds of lives, while California once again suffered record wildfires.
If you think that these things are regular, then you are right. We are the first generation to experience different weather types. These weathers are clearly deviating from what our grandparents, their grandparents, and grandparents of the previous generation experienced. New weather is caused by human-induced climate change. From hurricanes to summer rainfall, every weather event occurs under completely different environmental conditions than it did 250 years ago.
Climate change has gone from a vague future threat to a daily experience. It is already evident that the global average temperature is slightly 1 degree Celsius higher than it was before industrialization, the concentration of carbon dioxide in the atmosphere has exceeded 400 parts per million, the sea level has risen, and extreme weather events are more frequent and intense. These changes not only make weather more extreme, but also threaten decades of development gains and put the social and economic well-being of regions and countries around the world in imminent danger.
How humans change the weather
The impact of a process that began 250 years ago can still be deeply felt by people living in the present day, when in a laboratory in Glasgow, Scottish mechanical engineer and inventor James Watt invented "a new way to reduce steam and fuel consumption in fire engines". He and his steam engine paved the way for mechanical power and locomotives, and also awakened humanity's greedy thirst for coal, oil and gas. Since then, hundreds of millions of tons of fuel have been mined from the ground and burned in power plants and vehicles, making the planet heat up like a greenhouse.
Since James Watt's invention, the Earth's temperature has risen by 1.2 degrees Celsius. Carbon dioxide emissions initially increased slowly, but then accelerated by industrialization. Correspondingly, before 1960, the average global temperature rose slowly by only 0.2 degrees Celsius, and today the whole world is 1.2 degrees Celsius hotter than before. The hottest years were 2020 and 2016, and the past seven years have become the hottest seven years on record. However, the 1.2 degree Celsius increase in global average temperature is only an abstract measure. We don't notice it directly, we just feel its consequences. Changes in global average temperatures don't kill people, but they do.
This rise of 1.2 degrees Celsius has had a significant impact on our weather. Because Earth's atmosphere is closely connected through the global cycle, temperatures rise in almost every region of the planet. In the simplest case, the likelihood of a heat wave sweeping the world increases due to ubiquitous warming, while the likelihood of a cold wave occurring decreases.
Similarly, when the air becomes warmer, it can lock in more water vapor before the moisture condenses and clouds form. This moisture can stay in the atmosphere and clouds for days. But if the relative humidity exceeds 100%, it will fall in the form of rain and snow. Here's a simple formula: the more moisture the air absorbs, the more rain it will rain. This does not mean that no matter where we are, we will experience tropical rainstorms. The amount and intensity of rain is only rising at the global average level, with rain falling more in some places and possibly less in others. However, while warming has led to more heavy rains everywhere, average rainfall varies very differently worldwide.
Climate change is also affecting the weather in another way. Greenhouse gases not only make the atmosphere warmer, but also change its composition, changing the atmospheric circulation by adding carbon dioxide, methane, and water vapor, as humans have done. What we are changing is when and where the high and low pressures form, where they go, when and where it rains, the force of the wind, the season of wind and the direction in which the wind comes from.
These changes have consequences. Hurricanes are now in places where they were previously impossible. The oceans get hotter, and for the first time, water temperatures in some places have exceeded certain thresholds and become so warm that they are warm enough to provide energy for the formation of tropical cyclones. For centuries, we've experienced weather that's been within a stable climate — but as global warming, some well-known patterns of rainfall, drought, and storms are being upended.
But it's a global picture. Most people — from poor farmers to world leaders — want to know how climate change is affecting the weather where they live or where their assets are located. That's exactly what my job is about.
Linking extreme events to climate change
Until recently, if you asked a climate scientist if extreme weather events — heat waves, floods, droughts — were linked to climate change, the answers you heard might have disappointed you. Science can't find a correlation between the two, and the most we can say is that as the planet heats up, a particular event will happen more and more as we expect.
Thanks to attribution science, this has changed. For the first time in history, we have a way to make reliable statements about individual weather events. In a way, we've completely changed climate science: we're replacing uneasiness about weather causes with facts that we haven't done in the past. For the past 30 years, climate researchers have been talking about general climate processes, and now we can focus on the events that affect us here and now.
Extreme weather attribution is the search for weather disasters in a fictional world. When an extreme event occurs in the real world, we can define the event very precisely, knowing what we are looking for: what temperature, how many days it lasts, and so on. We can then create a computer model of the Earth where humans have not yet changed the climate through greenhouse gas emissions as a basis for understanding whether extreme weather events are affected by climate change. To do this, we simulate possible weather in a virtual world and then compare it to what might be in the real world in a real world that has warmed up 1.2 degrees Celsius. We then searched across two worlds to see how many simulated weather models met the definition of an extreme event.
What does this really mean? First, we determine what weather is possible in a particular region of a world that is heated by human activity. For example, how hot would the Pacific Ocean in the north-west of North America be in a typical summer? In a world that has warmed up to 1.2 degrees Celsius, the hottest day we just experienced this summer happened every ten years? Or every 50 or 100 years? How likely is the extreme heat wave we experienced likely to occur? We then asked the same question again, this time simulating possible weather in a virtual world without climate change. If a certain weather event is more likely or less likely to occur in a certain situation, it is clear that the difference is due to climate change; this is the only difference between us simulating weather conditions in two worlds. For example, if an extreme event occurs every ten years in our current climate, and once in a century-old world without climate change, then climate change makes the event occur at 10 times the frequency.
In the world of weather attribution — a cross-university project founded in 2014, I'm one of the leaders — we do attribution research in a matter of days or weeks — and sometimes a weather event isn't over. In recent months, in addition to the heatwaves in North America, we have assessed how climate change relates to flooding in Western Europe and a frost that caused a failed harvest of Grapes in France. We are studying the severe drought that occurred in Madagascar and studying its impact on it.
Although we can study events very quickly, we are not the only ones doing event attribution research. The Carbon Bulletin website's database lists more than 400 attribution studies, including many on floods, droughts, heat waves and other events in China. About 10 percent of these studies found no association between climate change and weather events. This does not mean that 10% of events are not affected by climate change, as not all events have been studied for attribution, but it suggests that the benefits of conducting attribution analysis are better than assuming that greenhouse gas emissions are responsible for every weather event. Extreme weather is often made worse by human activity, but sometimes it's just normal weather phenomena, or pure bad luck.
The implications of attribution science for planning and litigation
This new science answers the question many people want to ask when extreme weather occurs: Is climate change a contributing factor? But it's not just a tool to satisfy curiosity — it also has important practical implications.
One of the consequences of understanding how climate change affects the weather is that it allows officials and investors to ensure that our world is better prepared for the climate of the future. Investments in disaster prevention and management can only be effectively deployed if we know which weather events are more likely to occur in which seasons and geographies.
This saves lives and preserves prosperity. When people make plans — regardless of topic and scale — they focus on risk and cost. They also need to know what risks they are willing to take. But in order to do that, they first need to know exactly what the risk is. As the world warms up, many risks — such as a rainstorm large enough to wash away a river embankment — are changing from something rare and perhaps a 300-year occurrence to a more frequent one, such as an 80-year occurrence. Planners may only fortify cities for events that are more frequent than once in a century, and now they need to know the possibilities of these changes and act on extreme events that were unlikely to occur in the past.
Attribution isn't just a tool for understanding what's happening right now: it can also tell us how the likelihood of extreme weather is changing, and what we might encounter as the world continues to warm. The methods we use to calculate how climate change will change the weather are not just for the past. We can compare the real world to a world without climate change and the world of the future — allowing us to simulate the weather of the Earth in a scenario of varying degrees of heating, showing the consequences of continued greenhouse gas emissions for future risks. But while these tools already exist, many urban planners have failed to embrace them and the new challenges brought about by climate change. In my native Germany, the devastating floods that occurred this summer are a clear indication that we are not adequately prepared for today's extreme weather events, let alone future ones.
The second thing that attribution science can apply is that it is likely to be used in legal cases where weather changes are held accountable. In the future, we will see more and more energy companies being subpoenaed to court. The first lawsuits based on extreme weather events, rising sea levels and their links to climate change have been launched. With the help of attribution studies, the companies will be forced to compensate those who are not backed up by lobbying forces for the cause of climate-related damage.
This approach began in Kivalina in 2009. Kivalina is a village in northwestern Alaska that is home to 400 Inupiats. Kivalina often encounters blizzards in winter. For a long time, a barrier of sea ice provided it with protection. But climate change has caused those barriers to melt, with winter snowstorms submerging villages in the sea and eroding coastlines. As a result, the village's buildings are in danger of falling into the Bering Sea, and residents are forced to find their homes again. Villagers felt that some people and companies were responsible for this and filed lawsuits against them, such as oil company ExxonMobil and coal company Peabody Energy. The plaintiffs argue that the companies are deliberately deceiving the public about the climate impacts caused by burning fossil fuels. In addition to accusing them of providing false information, the case adds a new perspective: compensation for lost villages.
The lawsuit ended in failure because the court held it the responsibility of the U.S. Congress rather than the court, and the court was unable to determine the cause of the village's demise — but as attribution science evolved, the likelihood of successful litigation against these polluters increased. Some recent studies have calculated financial losses from specific extreme events that can be attributed to climate change. For example, recent studies have found that human action-induced sea-level rise exacerbated the damage caused by Hurricane Sandy on the East Coast of the United States in 2012, causing an additional $8.1 billion in damage. Another study found that climate change is responsible for $67 billion in damage caused by Hurricane Harvey in Texas in 2017. Previous lawsuits have ignored such analyses, partly because of the lack of specific figures and partly because parties and judges lack awareness of the latest science. Combining this with evidence of climate change liability can bridge the gap, and courts need the information to make awards of compensation for damage caused by extreme weather events.
Who will bear these losses? One answer is fossil fuel companies. According to research by California geographer Richard Head, 90 entities contributed 63 percent of global greenhouse gas emissions from 1751 to 2010. Half of those emissions only entered the atmosphere in 1988 – after the establishment of the Intergovernmental Panel on Climate Change (IPCC), we all realized that climate change exists, that it is a threat and can be measured. Head's carbon inventory can be used to determine the specific contributions of individual firms. According to the list, Saudi state-owned energy company Aramco and U.S. oil giant Chevron and ExxonMobil are each responsible for more than 3 percent of global greenhouse gas emissions since industrialization. BP, Gazprom, Royal Dutch Shell and Petro-Iranians are each responsible for more than 2 percent. We know the impact of these emissions on global average temperatures, which means we can complete the chain of causal evidence that allows oil giants to take responsibility for climate change and distribute the blame equitably.
Another approach is to focus on the state. While it is difficult for statistical firms to account for climate change, it is easier to calculate national responsibilities because such emissions reports are available worldwide. Depending on whether emissions are calculated since industrialization or more recently, we find that about one-third or two-fifths of the current warming is caused by emissions from the United States, the European Union and China.
Wherever you look, climate change is taking a clear toll: Bangladesh, the U.S. East Coast, the small island states, and Indonesia, a country with a large number of lowlands, suffered a severe tsunami in October 2018. In light of this, it is even more shocking that this issue has rarely been talked about for a long time, and has rarely played a role in so many years of climate change summits. But the damage caused by climate change is increasingly being translated into economic losses, and everyone knows the amount of damage, and politicians around the world will be under pressure to find solutions.
I wouldn't risk predicting what effect such a climate lawsuit would have in the future. But one thing is certain: the topic of discussion will shift from how rich countries and companies need to help poor countries to how to overcome the effects of climate change. Countries and businesses that are not serious about reducing greenhouse gas emissions should be most concerned about potential legal action.
Consequences of sustained emissions
Extreme weather attribution is a huge step forward in understanding our world. It allows us to answer some fundamental questions about events that have caused more and more devastation; it has helped prepare planners for a world that is hotter and more dangerous than it is today; and it may have opened the way for victims of extreme events to seek reparations. Attribution links real-world experiences to climate model predictions.
But perhaps most importantly, it tells us about the choices the world has made in recent decades and the choices we face today. For decades, it has been difficult for policymakers to completely ignore climate science, especially after the first intergovernmental climate change report was released in 1990. Yet in the face of growing evidence of the consequences of global warming and increasingly reliable projections of cost of losses, many continue to do nothing.
Attributive science makes this ignorance all the more untenable, connecting the past, present, and future, illuminating how we got where we are now and what we face as a result of decisions made now and in the near future. It's only warmed up 1.2 degrees Celsius, and the world has begun to experience deadly events that have never been recorded before, something that really couldn't have happened in the pre-industrial climate. Further warming will put more people around the world at risk of an unprecedented catastrophe.
Climate scientists foresee these changes over decades, and emissions continue to grow every year. Over time, problems have worsened, and catastrophic weather events have proven scientifically correct. The worst cost is borne by these people: people in developing countries, people working outdoors, people who can't afford insurance, they're always paying. The incremental costs will be borne primarily by those who were not yet born in the 1960s, 70s, 80s and 90s, when influential people chose to ignore climate change.
As long as the amount of greenhouse gases emitted into the atmosphere continues to increase, global temperatures will continue to rise. Once net zero CO2 emissions are achieved, temperatures will soon stop climbing. This brings a glimmer of hope, but it also puts pressure on governments and major businesses. The risks to everyone from increasingly extreme weather are clear; we are also seeing the benefits of rapidly reducing greenhouse gas emissions. But before all of this is achieved, the world will step further into the dangerous unknown.
(The author, Frederick Otto, is a senior lecturer at the Grantham Institute for Climate Change and The Environment at Imperial College London; Dr Frederick Otto was named one of the 100 most influential people in the world by Time magazine in September.) She recently joined Imperial College London's Grantham Institute for Climate Change and the Environment as a Senior Lecturer. Previously, she was Associate Director of the Institute for Environmental Change at the University of Oxford. She is the co-founder of World Weather Attribution, which conducts quantitative research on the impact of climate change on specific weather events; translator: Wei Jiang; Editor: Zhou Hao)
