Abrupt climate change evokes among many the fanciful image of New York City instantly frozen solid. This scene from the Day After Tomorrow was inspired by the real and sudden Younger Dryas event that plunged the North Atlantic into a millennium-long deep freeze 12,000 years ago. Although scientists have recently downgraded fears that this kind of event might happen today, abrupt climate changes are a more immediate threat than anyone knew.

It turns out that abrupt climate change isn't just applicable to massive events like the Young Dryas cooling but to regional or local abrupt changes too. Think drought. A recent study authored by Gemma Narisma (available here) and colleagues at the Center for Sustainability and the Global Environment (full disclosure: we are employed here but did not take part in this study) discovered about thirty abrupt changes in precipitation around the world over the last hundred years. Everybody has heard of the U.S. dust bowl in the 1930's and many know the catastrophic drought in the Sahel during the 1960's and 70's. But what about the droughts in the Former Soviet Union in the 1930's or those in Southern Africa in the 1980's that also claimed millions of victims?

These droughts aren't simply a random string of years that happened to have little rain. They are a persistent situation where the climate regime jumped from a normal or wet-stable state to a dry one. The abrupt droughts identified by Narisma et al. lasted for at least 10 years and majority had a 10% decrease from 20th century average rainfall. Most of the droughts occurred in arid or semi-arid areas already perched precariously on the edge of livable climates, where slight deviations from normal can have devastating consequences on the ecology and people that live there. A 10% decrease in rainfall might not sound like much, but it's enough to devastate crops, livestock, and livelihoods. In the Sahel, over one million people died, and 50 million people were affected by the change in rainfall, which according to the study decreased by 12% and lasted 17 years.

Abrupt climate change is inherently unpredictable. Although we'll never have perfect knowledge on who will be hit, we can at least learn who is most vulnerable and what we might do about it:

By identifying diverse regions around the globe where rapid climatic shifts have taken place, the study opens up new opportunities for understanding why these changes happen and what makes areas susceptible to them, says Narisma. A range of factors is likely involved, including human activities, such as deforestation and land degradation, and natural phenomena, like sea surface temperatures. The work might also lead to interventions that would make systems less vulnerable to sudden climate change, Narisma adds. (link)

This new bit of knowledge reinforces three increasingly recognized points:

First, we need to give more attention to climate change, especially abrupt change, on the scale of human lives. Too much talk about global average temperature detracts attention from the ways climate change manifests in particular places. Studies like this one help us understand how small perturbations can cause the climate system to cross the thresholds that bring on abrupt changes. Narisma et al.'s study, for instance, lends support to dynamic climate-vegetation models that include feedbacks between the land surface and the atmosphere. Under certain circumstances, a little more grazing or a bit more deforestation can induce large shifts in the regional climate. Regardless of the mechanism for the change, reducing vulnerability while increasing the capacity for adaptation and mitigation are key to persevering through change.

Studies of the magnitude of Narisma and colleagues', however, would be impossible without an extensive network of climate monitoring stations. The second point is to therefore give 'mundane' monitoring the attention it deserves. Unfortunately, the number of climate monitoring stations around the world increased throughout the 20th century until around 1980, when the number of stations began their precipitous decline and now there are about as many stations as there were in 1900. Without these local measurements, it becomes much more difficult to produce the kind of place-based information that can help decisions on the ground. While satellite monitoring has picked up part of the slack, some types of climate data are impossible to sense remotely. As we become more vulnerable to abrupt changes, now is the time to bolster our monitoring network. And we can. From ice cores that are used to reconstruct climate from long ago, to distributed networked devices that monitor local conditions, to autonomous environmental sensing spimes of the future, collecting and analyzing environmental data across the globe is crucial to seeing the big picture.

No amount of monitoring, however, will change the fact that abrupt climate change is inherently unpredictable, which brings us to the third point: we must get over the idea that climate adaptation plays second string to climate mitigation of greenhouse gases. Climate skeptics are right when they say the climate has always been changing. But they are completely wrong in their conclusions that we need neither mitigate nor adapt. We need to flip this dubious card on its head. Knowledge that abrupt climate change, and natural disasters in general, have wrenched past societies into disarray makes the climate question more, not less urgent. Global climate change only compounds an already painful history and strengthens the case to build resilient societies.



(The above animation from Narisma et al. shows abrupt droughts that have occurred worldwide over the last 100 years.)

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