Guest Blog: Where has all the warming gone?
Whether you are a climate scientist or not, it’s interesting that global temperatures rose so quickly from 1970 to 2000, yet haven’t changed for the past 15 years. If all these nasty greenhouse gases are on the rise, why isn’t temperature also increasing?
By David Hastings, Ph.D
“Where has all the warming gone? Long time passing …” Peter, Paul, and Mary’s refrain echoes through the blogosphere, as global temperatures have remained more or less flat for the past 15 years. It’s true! Global temperatures haven’t changed much since the record setting year of 1998.
The climate skeptics leapt on this fact a while ago, eager to discredit the overwhelming majority of climate change scientists and the vast troves of data indicating the severity of human-induced climate change. As usual, the skeptics missed more than a few key points, among them the fact that global temperatures are now at record highs; climate is by definition assessed with long-term (30 year) averages and not with year-by-year accounting.
An interesting spin-off has been the recent flurry of concern in The New York Times and The Economist that previous estimates of climate sensitivity were all wrong. The answer to “How hot is it going to get?” is incredibly important and everyone wants to get that question right. After all, if the earth isn’t warming as fast as we think it should be, perhaps we can continue our carbon-guzzling habit(s).
So, what’s going on? Whether you are a climate scientist or not, it’s interesting that global temperatures rose so quickly from 1970 to 2000, yet haven’t changed for the past 15 years. If all these nasty greenhouse gases are on the rise, why isn’t temperature also increasing?
A recent article by British and US climate scientists reminds us what we’ve known for a while, but sometimes forget: even though we care most about the air temperature, it’s the ocean that controls the planet’s heat, not the atmosphere. If you’ve ever wondered why coastal Seattle is cooler in the summer and warmer in the winter than Spokane, the moderating effect of ocean water is the reason.
Water holds a lot more heat than air. Your high school physics teacher would say water has a high heat capacity. And she’s right. So while global air temperatures may not have changed over the past 15 years, the temperature of the ocean has. In fact, warming of the deep oceans has been unprecedented over the past 50 years and is accelerating. And that’s what matters, since the ocean takes up more than 90% of the warming.
This May 10, 2013 study published in Geophysical Research Letters showed that winds blowing over the ocean have driven the heat into the deep ocean. We’re talking where the light don’t shine, and (most) fish don’t swim, below 700m, or over 2,000 feet. The reason could be due to changes in the Pacific Decadal Oscillation, which is a 20-30 year natural cycle.
So while the authors state: “the exact nature of the wind influence still needs to be understood…” we do know that the excess heat is going into the ocean, and that planetary global warming has accelerated, not stayed constant, as the skeptics would like us to think. This is simply scientists being conservative, which is normal, combined with a keen interest in continuing to work on the problem.
Another big, unanswered question is whether the uptake of excess heat into the oceans will slow down. We predict it will, but when?
The answer, my friend, is blowing in the wind which, of course, Bob Dylan knew all along. We should listen more carefully.
David Hastings is a marine geochemist at Eckerd College, St Petersburg, FL. His research interests focus on marine indicators of past climate change and climate change education.