Precipitating a Change

Video: Relative Changes in Precipitation (1:21)

IPCC Figure SPM 7. Relative changes in precipitation (in percent) for the period 2090–2099, relative to 1980–1999. Values are multimodel averages based on the SRES A1B scenario for December to February (left) and June to August (right). White areas are where less than 66% of the models agree in the sign of the change, and stippled areas are where more than 90% of the models agree in the sign of the change.

Click for a video transcript of "Relative Changes in Precipitation".

DR. RICHARD ALLEY: This figure is from the IPCC. And it's showing precipitation, rainfall, in the future for a moderate warming scenario. And on the left here is December, January, February. This is winter. And on the right here is maybe of more interest, this is summer.

And so this is showing how much water will come out of the sky. Things will look drier than this in a warmer world because evaporation will go up. In general, what you'll notice-- let's just look at the one on the right here, from summer. And sort of these redder or oranger areas down in here are going to be drier in the summer. And these bluer areas in the middle, then, are going to be wetter in the summers, as up in here at the poles as well.

And so what you generally tend to find is that the wet areas get wetter and the dry areas get drier. But in the modern world, we grow a lot of food in these places that are going to get drier. If you add in the rain will evaporate faster and that when it comes, it will fall really fast and tend to run off more, there's real worries about drought in the future.

Credit: Dutton Institute. "EARTH 104 Module 5 Future Rain." YouTube. January 23, 2015.

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.

This slightly complex figure shows projections of future precipitation. In general, the models project that wet places will get wetter, dry places dryer, and the dry subtropics will expand somewhat into currently wetter regions toward the poles. Evaporation is also expected to go up with warming, and many of the models find summertime drying in places we grow much of our food, so agriculture may be reduced more than you might think from looking at this, as we discuss after a quick look at sea level.

LOTS of other issues come up because climate affects so many things that we care about. A few of the larger issues include sea level rise, more floods and droughts, agriculture impacts, and impacts on people.