[ECAR Summer 2008] Kevin Trenberth – NCAR – Global Warming Affects us all: What must be done?

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The IPCC report stating that warming of the climate is unequivocal and very likely caused by human activities was a remarkable demonstration of the strength of the evidence – passed by 130 nations.

Increasing CO2 – has a lifetime of 100 years before it gets taken out of the system. US continues to increase – 20% increase since 1990. China now represents a big and growing percentage of CO2 emissions. If we make gains in western world, will they be overwhelmed by the emerging world? There is pressure to look at emissions per capita rather than by nation. Western Europe is 2.5 x better than US – is that due to higher gas prices? Highlights the fact that population is a big part of the equation, but nobody is talking about that.

There are also differences between states – California vs. Texas, for example.

Evidence – sea level is rising – 48 mm since 1992 (as measured by satellites). Might be best measure. Glaciers are melting, even as snowfall rises. Snow season is getting shorter – meltoff in Pacific Northwest is 7-10 days earlier now. Risk of drought increases substantially, along with wildfire danger.

Everything that’s going on in climate has a natural variability component and a global warming component.

Modeling the climate system is complex. Need computers that are 10,000 times faster than those we have now to accurately model. Shows a slide that models global temperatures that accounts for the real observations by adding human effects to what would have occurred naturally.

Precipitation patterns change – the wet places get wetter and more intense, the dry places get dryer.

What do we do?

Mitigation, adaptation, or do nothing.

Doing nothing == adaptation without planning.

What you do relates to value systems. That’s where politicians get involved.

The UN Framework Convention on Climate Change (ratified in 1994, including by US). Kyoto Protocol is a legal instrument under that convention. US withdrew in 2001. In 2004 US emissions were 16% over 1990 levels for greenhouse gasses.

What about a carbon tax? If there was a value to CO2 presumably the production of CO2 as waste would be reduced. Cap and trade is a variation – favored by Congress at present (at least partly because it doesn’t have the term “tax” in it). Tracking sources of violators becomes a whole new industry. If countries don’t subscribe it can favor those who pollute.

Coal fired power plants have been brought online at a rate of 2 per week over the past 5 years. China leads with one every 3 days or so.

A freeze on emissions means that conventrations of CO2 continue to increase. We have to adapt to climate change.

Assess vulnerability; devise coping strategies; determine impacts of possible changes : we need information!

We need to observe and track climate changes as they occur; analyze global products with models; understand the changes and their origins; validate and improve models; initialize models and predict futue developments; and assess impacts so as to provide advice.

Weather prediction – a problem of predicting the evolution of the atmosphere for minutes to days to perhaps 2 weeks ahead. Begins with observations of initial state ; atmosphere is a chaotic fluid, small uncertainties or model errors grow rapidly in time and make longer term prediction impossible.

Climate prediction – problem of predicting the patterns or character of weather and the evolution of the entire climate system. Often regarded as a “boundary value” problem This means determining systematic departures from normal from the influences of the climate system and external forcings. The oceans and ice evolve slowly, providing some predictability on mult-year time scales. Because there are many possible weather situations, it is inherently probabalistic.

As time scale is extended, the influence of anomalous boundary forcings grows to become noteworthy. The largest signal is El Nino. involves knowing the state of the ocean. All climate prediction involves initial conditions of the climate system, leading to a seamless (in time) prediction problem. A challenge we’re not capable of meeting at the present.

There have been no revolutionary changes in weather and climate model design since the 1970s. The models are somewhat better. Meanwhile, computing power is up by a factor of a million. That’s gone to increasing resolution of models and longer runs.

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