The summer solstice is here, and it’s historically hot again in the northern hemisphere. Millions of people have been under heat watches in the U.S. Parts of Europe are experiencing record-setting temperatures. And this spring South Asia had one of its most severe heat episodes on record. While the increasing frequency and severity of extreme heat may be shocking, it should no longer be surprising — this is what it means to live in a world that has warmed by more than 1 degrees Celsius globally.
There is now very clear evidence that global warming is increasing the frequency and severity of many kinds of extremes, including events that are so hot they are unprecedented in our historical experience. In fact, scientists have already determined that global warming made the severe heat in South Asia 30 times more likely. Research has shown similar results for other recent heat events, including the record-shattering heat wave in the Pacific Northwest last year.
This intensification from global warming is now broadly true around the world: Overall, the level of heat that used to occur once in a half century is now likely to occur five times as often, and global warming has already increased the odds of unprecedented heat events across most of the globe. So, if it seems like every summer is treating us to another spate of heat-related disasters of historic proportions, well, that’s because it is.
While there is of course variability from place to place and year to year, the increasing frequency of these kinds of record-breaking heat events are a fundamental feature of global warming. And that means that we can reliably expect these trends to continue.
Unfortunately, increases in severe heat carry severe risks. In addition to the mountain of studies showing that hot events are intensifying, there is also very clear evidence that severe heat impacts people and ecosystems. These impacts include the direct effects of hot temperatures on human health through heat stress and other heat-related illnesses. They also include indirect health effects from labor injuries, poor air quality and mental health (including suicide). Multiple lines of evidence also show that high temperatures affect cognitive performance, labor productivity and economic growth, as well as interpersonal and intergroup conflict. And poor and marginalized people and communities are both more exposed and more vulnerable to these effects.
Heat also causes steep declines in agricultural yields, costing billions of dollars in the U.S. alone. Further, recent research shows that global warming has increased the odds that different breadbasket regions around the world experience severely hot conditions in the same year, elevating the risk of the kinds of supply shocks that exacerbate food insecurity. And the plants we grow aren’t the only plants that are vulnerable: Severe heat exacerbates drought conditions, dries out vegetation leading to larger and more severe wildfires, and it has been implicated in forest die-off events around the world.
To make matters worse, these impacts are not limited to plants and animals on land. Last summer’s Pacific Northwest heat wave was estimated to have killed as many as 1 billion marine organisms. Similar “marine heat waves” have impacted other ocean ecosystems around the world, including massive coral die-offs in reefs around Hawaii and Australia’s Great Barrier Reef, which is currently experiencing its fourth mass bleaching event in the last seven years. Globally, marine heat waves have increased 50 percent in the last decade, and are now 10 times as severe due to global warming.
There used to be a time, not too long ago, when the urgency of global warming was framed in terms of avoiding dangerous impacts in the future. What has become increasingly clear — in the scientific literature and in our lived experience — is both that climate change is impacting people and ecosystems here and now, and that the impacts are often non-linear. That is, all else being equal, we can expect the next degree of global warming to do a lot more damage than the degree that’s already happened.
But all else doesn’t need to be equal. Because human activities are the primary cause of global warming, human activities will determine how much additional global warming there is in the future — whether that is the additional 1.5 degrees Celsius implied by current policies and actions, or the much more ambitious targets agreed upon in the UN Paris Agreement (and now committed to by so many countries, corporations, and institutions around the world, including our own university, Stanford).
In addition, we also have control of how we respond to the climate change that is happening. This means preparing for the world that we now live in — a world in which extreme events such as record-setting heat waves are not a surprise, but a routine occurrence. For instance, we can ensure that individuals — especially the most vulnerable — have access to places to stay cool (either inside their homes or in their communities), that energy systems remain functional during extreme heat events, and that public health systems are prepared for surging demand for health services.
Absent these actions, some version of this perspective — in which researchers emphasize that the frequency and magnitude of extremes are increasing, the impacts are getting worse, and the risks are intensifying — will likely be published again about this time next year. And the year after, and the year after that, in increasingly amplified, histrionic form as scientific evidence continues to mount and people’s experience continues to become more acute.
Survey evidence from the U.S. and globally suggests that substantial majorities of people already think that climate change is an emergency, and that they support increased action from government, corporations and citizens. As climate researchers, we will continue to gather more evidence, and will continue to share our perspective to communicate the results. But until action is taken, it’s not clear what more or new there is to say.
Noah Diffenbaugh is the Kara J Foundation professor and the Kimmelman Family senior fellow in the new Stanford Doerr School of Sustainability.
Marshall Burke is an associate professor in the new Stanford Doerr School of Sustainability, as well as a fellow at Stanford’s Center on Food Security and the Environment.