Vicky Pope responds to critics of computer models for climate

Today, a climate scientist in the U.K. responds to critics of computer modeling. Critics claim that if forecasts of weather just days away are often wrong, how can scientists claim to know what climate will be like 50 years out?

Vicky Pope: We can look at the range of possible outcomes. We’re not saying that there is only one possible future if you do a particular emissions level. We’re saying that there’s a range of possible futures, and that range is representative of the uncertainty in the science.

Vicky Pope is talking about the range of possible risks of climate change. She heads climate change science for the Hadley Centre of the Met Office, the United Kingdom’s national weather service. The Hadley Centre produces some of the world’s most-used climate models. They crunch numbers that simulate the processes that drive Earth’s climate, like incoming sunlight and the circulation and composition of the ocean and atmosphere.

Vicky Pope: The models are based on the laws of physics. So they’re solving the equations that represent those laws. We also run the model every day as a weather forecast. We test it that way. And we compare models of past climate with the observed climate, not just in terms of temperature, but in terms of the physical processes that are important for climate change – like cloud feedbacks, for example.

Dr. Pope said that computer power is the main limitation in simulating in finer detail of climate at a more local scale. She said the long-term models aren’t perfect. Scientists are continually improving them. But these models are the best humanity has for predicting future climate.

EarthSky asked Vicky Pope what she felt was most important for people to know today about climate change.

Vicky Pope: I think it’s important that people understand how much we need to reduce emissions and as quickly as we need to reduce emissions in order to avoid the impacts of dangerous climate change. It’s only if we can peak emissions in the next ten years and reduce at about four percent per year that we’re going to stand a 50-50 chance of limiting temperature rise to two degrees, which would avoid the worst impacts.

Dr. Pope spoke about what she and other scientists see as ‘dangerous’ climate change.

Vicky Pope: The dangerous climate change is different for different people, in different parts of the world. And it’s important that we understand these sort of implications. It’s not a question of reaching a particular threshold and then everything falls apart. It is a gradual change, but we need to be looking out for where does a particular change become irreversible? For example, if the rainforest starts to die, can it recover if temperatures go back down again?

There is also, said Pope, a commitment to climate change from the greenhouse gases, which can persist in the atmosphere for over a hundred years.

Vicky Pope: If we stabilize temperatures to a particular level, it might be that we haven’t started to see any change in that particular aspect of climate or ecosystem. But if we keep the temperature constant, that it continues to change. So again using the Amazon rainforest as an example, at two degrees, we don’t see an impact of climate change. But if we keep the temperature at two degrees, we do start to see an Amazon die-back. That’s an example of commitment. So irreversibility and commitment, I think are really important when looking at dangerous climate change.

May 10, 2010

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