Warming around the Globe

Video: Projected Surface Temperature Changes (2:55)

IPCC Figure SPM 6. Projected surface temperature changes for the early and late 21st century relative to the period 1980–1999. The central and right panels show the AOGCM multi-model average projections for the B1 (top), A1B (middle) and A2 (bottom) SRES scenarios averaged over the decades 2020–2029 (center) and 2090–2099 (right). The left panels show corresponding uncertainties as the relative probabilities of estimated global average warming from several different AOGCM and Earth System Model of Intermediate Complexity studies for the same periods. Some studies present results only for a subset of the SRES scenarios, or for various model versions. Therefore the difference in the number of curves shown in the left-hand panels is due only to differences in the availability of results.

Click for a video transcript of "Projected Surface Temperature Changes".

DR. RICHARD ALLEY: This is a moderately complicated plot that comes from the IPCC, and we're going to look at a few things here. This is not much CO2 in the future relative to what's possible. And so you see how much warming might occur for the global average out to 2020 to '29, that decade, and how much warming might occur out at 2090 to 2099 in degrees Celsius, which are listed along the bottom here.

And then these maps correspond here on the right to the warming from 2020 to 2029, the average of that decade, and what you expect late in the century that we're in now for this low emissions. And then here's the same thing for somewhat higher emissions of CO2. More warming. And here's one where we really keep burning like crazy. I'm just going to walk you through that when all of them show about the same thing, but we'll start down there.

First thing to notice is that these are how much warming is possible by late in the century here, and they show probabilities. The highest point is the most likely, and then there's a slight chance of having low values like this or low values like this. What I hope you notice is that the warming could be a little bit less, or it could be a little bit more. Very, very unlikely to be a lot less, but it is possible to be a lot more.

And so there's a lop-sidedness in this. And if the scientists are wrong about what's most likely, then it's more likely that we'll get more warming. More likely more warming than what people have been telling you. OK. That's important first.

Second thing. The average warming here is just over 3 degrees Celsius, which is sort of this color, which is what you'd get out here in the ocean. Most of the world is ocean. The global average is not what happens on land where we live. It's what happens primarily in the ocean.

What you will notice is that all of the colors over here tend to be darker in red colors than what's in the ocean when you go up on land. Almost everyone on the planet gets above average warming because the land warms more than the ocean, and almost everyone lives on the land rather than in the ocean. So when people tell you the global average warming they expect, in some sense, that's very optimistic because it's the low end of what's possible, and it's mostly telling you what's happening where people don't live rather than where people do live.

Credit: Dutton Institute. "EARTH 104 Module 5 Future Maps." YouTube. November 19, 2014. Source: IPCC, 2007: Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

The figures here show the projected warming, and uncertainties. The maps are the projected warming for the next decade (2020-2029, center) and the last decade in this century (2090-2099, right), for different possible emissions scenarios, with more CO₂ emitted as you go down through the maps. The estimates were made with Atmosphere-Ocean General Circulation Models (AOGCMs), the big climate models of the world. And, the maps here are the averages of the projections from all of the models participating in this effort—tests in the past have shown that this average across all the models generally does better than any single model (the “wisdom of the crowd” in models).

Warming is projected to be especially slow in those places where ocean water sinks into the deep ocean, and especially fast in the Arctic. Projected warming is generally larger over land than over ocean. Because the Earth is mostly ocean, the numbers usually given for “global warming” are closer to ocean than to land values. But, almost everyone lives on land, so the great majority of people are expected to experience above-average warming!

The panels on the left show the uncertainties in the projected warming. Notice for the 2090-2099 projections (the larger warmings, in red), that the most-likely warming tends to be towards the low end of the possible warmings. We have already seen that the most-likely impacts of a specified warming are on the low-damage side of the possible impacts, and now we see that the most-likely warming is on the low side of the possible warmings. Both of these have the same effect: the less you trust climate scientists to get the most-likely estimate correct, the more worried you probably should be about climate change, because the numbers most frequently quoted by scientists are on the optimistic side of the possibilities.