Beyond CO2: an insider's view of climate change research

With greenhouse gases now almost synonymous with carbon dioxide in everyday usage, it is easy to forget that CO2 only accounts for 60% of climate warming and that climate is part of a complex earth-atmosphere system. Cambridge University climate change researcher Peter Braesicke tells Goska Romanowicz about the links between climate, pollution, the ozone layer - and how he manages to stay optimistic despite the signs of impeding doom he encounters in his everyday work.

Your work on climate change focuses on ozone - but most people don't even know that ozone is a climate change gas. Are we wrong to talk of carbon emissions as the only cause of climate change?

Carbon dioxide is still the most important climate change gas, because we have pumped out such enormous amounts of it and we still are. Also, it is being emitted in a non-homogenous way, so for example the US has a very important role while the importance of emissions from the developing world is growing exponentially. That's why we talk about it as the climate change gas in the press, and I think there are good reasons for that.

But of course other greenhouse gases like methane, nitrous oxide, ozone and others that contribute about 40% in total to the climate warming observed so far. And if you pump out other gases at the same levels the effects could be as severe or even more severe than CO2 if they pass a certain threshold.

This is because some of the other greenhouse gases are more effective in catching out the long-wave radiation and heating the earth, methane for example. They produce a stronger greenhouse effect per molecule but they are pumped out in smaller amounts, and so still have a weaker effect than CO2. But they are certainly not negligible.

Are the other greenhouse gases likely to increase in importance?

There are still large uncertainties as to the contributions of some of these gases, and aerosols. These are compounded by the fact that determining their effect is more than a one-stage process. As climate scientists, we use scenarios of what we will emit in the future. Economists and others develop scenarios of what we will emit in the future, and we take those the scenarios and put them into our climate models and see what happens.

Even though we have a good general idea of what's happening the details are still uncertain - there is no doubt that there is a significant amount of climate change but the exact details are quite uncertain.

Nevertheless it is encouraging to see that when you compare different models they give you very similar answers. This builds our confidence in our understanding and predictions.

Do you think that politicians misinterpret scientists' comments about the uncertainties in climate predictions?

Politicians take advantage of the uncertainties in climate change science. Bush, for example, took advantage of the honesty of scientists. We said that yes, we believe that in general the theory is true but there are uncertainties as to the detail. He interpreted this as the whole theory being uncertain, and we might not even be experiencing global warming at all.

The climate change models you use include not only a wide range of climate change gases, but also simulate the chemical interactions between them as they react, produce new gases, and are exchanged between the air, soil and oceans. Why look into all this complexity instead of a steady carbon dioxide increase?

Introducing chemistry into models makes them to some degree more accurate, it also adds more detail, and allows us to access other closely related effects of our emissions such as air pollution.

Air quality is strongly linked to climate change because air quality depends on factors like aerosol concentrations, photolysis, and temperature, which come under the causes and results of climate change. We find, for example, that if China doubles its emissions not only will it contribute to climate change but air pollution will be extremely severe, with many areas above the health threshold recommended by the WHO.

Overall, we can explore many more interconnections and look at the climate system as a whole by including chemical interactions and a range of climate gases - the depletion of the ozone layer and its recovery, for example, are certainly not isolated from climate change.

How is the ozone layer connected to our emissions at ground level, and to climate?

Climate change may either help or counteract the amount of recovery we see and on which timescales we see it. Because even though the ozone 'hole' may recover over the next decade or so, how it recovers may be very different depending on how strongly it is affected by climate change. As the climate warms the stratosphere [the region of the atmosphere that starts above 10-12 kilometres above ground] will become colder and that will affect chemical reactions that determine ozone concentrations. To get the timescales of the recovery right you have to look very carefully at the chemistry-climate interactions. Climate change won't stop ozone recovering, but it may change the detail of the timing of the recovery process.

Is this a two-way interaction?

Yes - ozone also affects the climate. We've seen good evidence that ozone and temperature trends have a very close link - we have seen very good evidence from models and observations that ozone trends go hand in hand with temperature in the stratosphere.

And other interactions that link climate to the earth system?

Oceans are also an important part of our research. There are implications for food - because if the climate is changing and the oceans are getting warmer fish stocks may be depleted because fish cannot find enough food in a warmer sea.

Do you think that as a scientist working in climate change research you more aware of the consequences of the changes we are producing?

I'm very aware of the consequences, and I want policy-makers to take action. I'm worried, but I also think that - like we did with the ozone layer - we are capable of identifying the problem and in the end acting upon it. I still see a chance and a way out.

And I hope that people being reminded day in day out about these consequences there will be some action taken, that some major changes in how we use and produce our energy will be made.

To stop ozone depletion we just had to replace a few chemicals used in fridges, air conditioning etc. - with climate change, we would have to entirely re-think our energy provision. Can you really compare the two?

Yes, climate is a more complex issue than ozone, but there are still ways and technologies to explore that may help us, and the process of identifying, researching and tackling a problem remains the same.

There are also other factors that add to the complexity - such as the fact that we have to be extremely careful about what we ask developing countries to do, as their emissions will become increasingly significant. A developing country wants to grow, wants to develop its industry and it has a right to come closer to the life standards that we enjoy in the West.

But we need to help them to grow in a sustainable way. There are already technologies by which we can generate energy from wind, tides, sun, water, and I'm pretty optimistic that the answer will lie in improving those.

Maybe I'm too optimistic, but I still hope that we can find a way to develop the global economy on a more modern and sustainable level eventually than rather than using the approach we has during the industrial revolution.

I understand that it's a big investment but if we don't make this investment then we should say goodbye and leave this planet.

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