By Jeremy Houser
It's been a wet, dreary week, with only the occasional glimpse of sun passing so fast I never found the time to switch from boots to sandals. Coming out of an April that saw 5.23 inches of rain (an inch more than the average April), it seems reasonable to think about how – or if – this rain is related to climate change. Climate and weather are distinct, yet deeply connected. Since the weather is such a large presence in normal life (humans have surely been talking about the weather since the dawn of language), it's only natural that for most people, questions about unusual weather are the most common entrance to a discussion of climate change. Though it's not always welcome: Last night during a TV broadcast of a baseball game one announcer rather whimsically wondered whether the weather had anything to do with global warming, to which his partner replied, approximately, “Don't go there!” Well, why not go there? Some thoughts on two questions:
First, is a very rainy April proof that climate change is real? Not really. Maybe just a tiny bit, but not really. I suppose I worry that in pointing out weather consistent with predicted climate change we inadvertently acknowledge some validity in the next round of global warming jokes that are guaranteed to accompany the next big snowstorm or cold spell. (These days it's easy to find someone – both in your own neighborhood and in the U.S. Congress – who can turn a foot of snow into a joke about Al Gore.) Relevant to this specific case, it's worth noting that March was just as dry as April was wet. Fortunately, this is a double-edged sword that this battle doesn't require wielding. For better or worse, we don't need confirmation from recent weather to know that climate change is real; we have decades of long-term climate data (and thousands of scientific studies) to demonstrate that.
Second, is it the result of climate change? Now that one's a little trickier. Over the past 50 years, average annual precipitation in New England has risen 5-10%, with most of that increase in the spring, summer, and fall. By the end of this century, precipitation is projected to rise another 5-10% in spring (and 20-30% in winter!), with little or no change in summer and fall. Also, more of our precipitation is expected to be concentrated in extreme downpours, nor'easters, and hurricanes. So climate change, in this case a region-wide increase in spring precipitation, certainly could be one factor (among many) in our rainy April. Maybe the best way of answering the second question is to take the perspective that climate change involves a change in the meaning of unusual weather, a “new normal” that is ever-changing: Was April unusually wet? Probably yes, but less unusual than it would have been 50 years ago. By the end of this century, 5.23 inches may not be unusual at all.
Jeremy is working with VCS on our Climate Initiative under a grant from the Edey Foundation.