What Are We Missing?

Shafiqul Islam

Professor, Civil and Environmental Engineering, School of Engineering

This year, in August, in Boston we had the least amount of rainfall in the last 120 years. Is this climate change? We do not know. This is only one year. There is a distinction that needs to be made between what is a change and what is a natural variability.

Climate is a long-term phenomenon. This notion of long-term can also be used as an excuse not to act. Because we can say, "This is just one event, so it might not happen again in the near future." But the key here is that we are changing the system. We've been doing it at an increasing pace over the last several decades. These changes will have consequences. We may not know, precisely, what the consequences are, but we do know they will have consequences because the climate system itself is non-linear and has a range of feedbacks. Climate is a complex and coupled land-atmosphere-ocean system. It will react, if altered, in a very unpredictable way. That part we do know. So we have to start working on how to really start mitigating some of these changes we are imposing on the climate system.

"We are changing the system. We've been doing it at an increasing pace over the last several decades. These changes will have consequences."

In our research group, what we're trying to understand basically is "Under diffeent scenarios, how will the distribution of water change across the globe?" In particular, "Is rainfall changing, if it's changing, how is it changing in space and time?" Is it changing because it becoming more extreme or has it become more frequent? And that has significant implications in terms of the US, because in the US, I think everybody agrees that rainfall has gone up. The question then is, how did it go up? Did it go up because it has become more extreme, or did it go up because it has become more frequent?"

Let's say that I have ten storms in a year. Out of those ten storms, say three are extremely heavy compared to climatological averages. That is a notion of extreme getting more extreme. Now, instead of ten say we have 20 storms, but the same amount of rain, so rainfall is getting more frequent. We need to understand whether extremes are getting more extreme or rainfall is getting more frequent.

"We need to understand whether extremes are getting more extreme or rainfall is getting more frequent."

I think sensational stories are emphasizing that climate is getting more extreme, but that is not very well founded in the literature. Think of the unusual drought this summer in Boston and very heavy rainfall in England over this summer. Are these two anecdotal examples part of a natural variability or are these signatures of climate change? We need to make a more robust distinction between natural variability and change, but given that climate is a non-linear and unpredictable system and we have already changed it significantly, we simply cannot wait to act to mitigate some of the human-induced changes.

[ Learn more about Islam's work ]

Interviews by Georgiana Cohen, Office of Web Communications

Homepage photo by John McConnico / Associated Press. Tseng photo by Melody Ko, University Photographer. Islam, Metcalf, Rappaport, Reed and Shimshack photos by Alonso Nichols for Tufts University. Portney photo by Zara Tzanev for Tufts University. Kirshen photo by Aaron Schutzengel (A'07) for Tufts University. Najam photo by Brian Loeb (A'06) for Tufts University.

This story originally ran on Oct. 22, 2007.