Warming to the Future

Video: Global Surface Warming (2:23)

Click for a video transcript of "Global Surface Warming".

PRESENTER: This is a plot from the IPCC from 2007, their fourth assessment. Down here, this is basically going to more CO2 as we go in the future.
And so these different things are scenarios for how much CO2 we face. This is the history of temperature going from 1900 up through 2000 and then the future of temperature as we look into the future.

The warming, to date, is sort of one degree. That's not terribly big. The uncertainty is somewhere between one degree Fahrenheit and one degree Celsius. And so the warming is sort of one degree.

If in the year 2000, we had stabilized the composition of the atmosphere, so no more changes happened in the air, we actually would have expected a little more warming, as shown on this orange curve down here, because the ocean has to catch up.

Right now, a lot of the heat is going from the air into the ocean. And as the ocean warms, the air will catch up. But not a lot more warming.
These others show various paths in the future, depending on how much CO2 we emit. So far, we're tracking very near or just above the uppermost of these. But we haven't gone very far yet.

Things to notice-- first of all, is it in all futures in which we don't do a lot to reduce CO2, the warming that is coming is very big compared to the warming which has happened?

Now, the world does not end in 2100. And you'll notice that all of these curves are still heading up, at least slowly and possibly rapidly, as we go into the future. Some students are going to live off of this graph.

You'll also notice over on the side that the uncertainties, as so often happens in this, are mostly on the bad side. So there's a most likely value. And it could be somewhat less or there's more room on the high side.

If it's more, it could be even more. And so what you see is that, if we don't do a lot to head off CO2 emissions, the warming, so far, is very small compared to the warming that comes, with the uncertainties mostly on the bad side.

IPCC Figure SPM 5. Solid lines are multi-model global averages of surface warming (relative to 1980–1999) for the scenarios A2, A1B, and B1, shown as continuations of the 20th-century simulations. Shading denotes the ±1 standard deviation range of individual model annual averages. The orange line is for the experiment where concentrations were held constant at the year 2000 values. The grey bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios. The assessment of the best estimate and likely ranges in the grey bars includes the AOGCMs in the left part of the figure, as well as results from a hierarchy of independent models and observational constraints.

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 figure shows the past warming, which is just under 1°C or roughly 1°F, together with the future warmings for the different scenarios. The lowermost future line assumes that the atmospheric composition had been stabilized in the year 2000, with no further rise of CO₂. Warming continues in that scenario because some heat is now going into the ocean, keeping the air cooler than it will be as ocean warming catches up. Note that it is already too late for us to follow that path because we have raised CO₂ since 2000. Also, we are committed to some additional warming if we choose to stabilize the atmospheric concentrations at any point in any of the scenarios, again because of the slow warming of the ocean.

In all the other scenarios, if we don’t make major efforts to reduce future CO₂ emissions, the future warming is projected to be quite large compared to the past warming, and the temperature is still going up as the next century starts. Also notice the uncertainty bars on the right, showing that warming may be a little less than the most-likely estimate, or a little more, or somewhat more than that.