WunderBlog Archive » Dr. Ricky Rood's Climate Change Blog

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By: Dr. Ricky Rood, 1:06 AM GMT on February 17, 2007

Was the last blog convincing or has climate change become uninteresting? The evidence for warming is broad and deep; we could go on and on. Temperature is both the easiest to predict and to measure. Water is, however, at the center of it all. The ability to exist in three phases, gas, liquid, and ice, is important to climate stability. Water supply is crucial to life and industry. And it is often not appreciated how important water is to the generation of energy. It is all about water.

In the climate system the phase changes of water are responsible for the uptake and release of energy. The meteorologists out there know this is important for, say, both middle latitude storms and hurricanes. When considering the climate, we also have to consider the role of water in the radiative balance of the planet. Water is a greenhouse gas. Clouds reflect solar radiation, and also contribute to the greenhouse effect because they help hold infrared terrestrial radiation near the surface. Hence, clouds and how clouds might change sit at the base of many of the uncertainties in estimates of global warming. And ice--ice reflects solar radiation magnificently, plus if ice is on the ocean or the ground it acts as an insulator between the air and surface. That's just the role of ice in the temperature budget; there's also the perspective of the water budget. It's all important; too big for one blog.

This figure is one of the iconic figures of climate science. This version is from the CERES web page. CERES is a space instrument which makes accurate calculations of the Earth's radiation budget. The brochure has a nice introduction to clouds and radiation.

Figure 1. From "CERES Instrument Brochure" This figure shows how solar (visible) and terrestrial (infrared) radiation behaves in the atmosphere. This is for equilibrium conditions - steady average temperature - input matches output.

The figure shows the long-term radiative balance of the Earth, where the incoming solar radiation is balanced by the outgoing terrestrial radiation. One of the takeaway messages from this figure is that the Earth's temperature is strongly controlled by things that reflect and things that absorb. Water in any form is important. This is a very rich figure, worthy of descriptive essays.

A controversial issue amongst scientists about the IPCC 2007 report is ice - and the melting of ice. In my career there are two things that have truly surprised me, and they both have to do with phase changes. The first was the presence of nitric acid clouds in the stratosphere; the second is our realization and growing understanding of how fast ice can melt. This rapid melting is strongly related to the coexistence of water and ice. Once there is water on and in large ice sheets, it flows. As it flows there is more melting and lubrication which accelerates the motion of the ice sheets "down hill" perhaps towards the ocean. We are just beginning to be able to model ice sheet dynamics and melting.

Some scientists think that we already know enough about melting that the IPCC report has significantly underestimated the melting of the ice sheets, and hence, sea level rise. Other scientists think that we cannot state with certainty that the current melting rates will be sustained for long periods of time; perhaps, there is an oscillation. Since the IPCC deals in what is considered most certain, since consensus is required, these legitimately controversial arguments are noted. The report states that if the recent trends in ice flow were to continue at the same rate, then sea level increase would be 0.1 to 0.2 meters higher than the best estimates. This is a classic example of the intersection between what we know, what we believe, and what we think we know. The IPCC deals in what we know.

A question at the top of everyone's list is how much water is in the ice sheets? From the point of view of sea level, the ice in Greenland translates to about 7 meters; Antarctica closer to 60 meters. We like to think in terms of incremental changes, but when we are dealing with phase changes, things can happen quickly.


There is an excellent tour of the Earth's ice at this NASA link. Be careful of all the megabytes.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.