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Conservation Science for a Healthy Planet

How we know it was climate change in record breaking hurricanes and wildfires in the US

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STANFORD, Calif. —

….My lab recently published a new framework for examining connections between global warming and extreme events. Other scientists are doing similar research. How would we go about testing whether global warming has influenced the events that occurred this year?

Consider Hurricane Harvey, which caused enormous destruction along the Gulf Coast; it will cost an estimated $180 billion to recover from the hurricane’s storm surge, high winds and record-setting precipitation and flooding. Did global warming contribute to this disaster? The word “contribute” is key. This doesn’t mean that without global warming, there wouldn’t have been a hurricane. Rather, the question is whether changes in the climate raised the odds of producing extreme conditions.

Hurricanes are complicated business. While there is evidence that global warming should increase the frequency of very intense storms, their rarity and complexity make it difficult to detect climate change’s fingerprint.

It is therefore critical to examine all of the contributing factors. In the case of Hurricane Harvey, these include the warm ocean that provided energy for the storm; the elevated sea level on top of which the storm surge occurred; the atmospheric pressure pattern that contributed to the storm’s stalling over the coast; and the atmospheric water vapor that provided moisture for the record-setting precipitation…..

….Our scientific framework can also be applied to other events. Like Harvey’s devastation, California’s ravaging wildfires arose from a confluence of factors. Strong, dry winds were the most immediate contributor. In addition, the protracted drought that killed millions of trees created substantial fuel. After the drought, an extremely wet winter was followed by severely hot, dry conditions in the summer and fall, which together produced near-record fuel for fires. Although each of these specific factors will need to be analyzed, we already know that global warming has increased fuel aridity in the West, meaning that fires are more likely to encounter large amounts of dry fuel.

There is now ample evidence that global warming has influenced extremes in the United States and around the world through such factors as temperature, atmospheric moisture and sea level. This doesn’t mean that every event has a human fingerprint. But it does mean that we can expect more years like this one, when our old expectations no longer apply.

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