Antarctic climate change – the exception that proves the rule?

Antarctica has been in the news recently because two large icebergs (one about 60 miles long and the other about 50) have broken off the continent. These “calving” events often occur naturally and these ones are probably not linked to climate change, although they might affect the global ocean circulation.

But I thought that this would be a good opportunity to have a look at the general climate situation in the South Pole region…

The clearest signal is rapid warming that has been seen on the Antarctic Peninsula (the bit that points up to South America) over the last 50 years.

The picture for the rest of the continent is not so clear, mainly because of the lack of data. For comparison, the USA has over 1000 climatological observing stations, some of which go back to the late 1800s; Antarctica currently has around 55 stations, very few of which go back to before 1957, (plus a similar number of automatic weather stations, which tend to not be maintained for long periods) and these data are used to represent a much bigger land area.

[Image from NASA]

Nonetheless, there have been some high profile studies looking at Antarctic temperature trends, some finding cooling, some finding warming and nearly all being controversial.

So why is the warming on the Peninsula so clear?

The reason is that the warming is mostly driven by atmospheric circulation changes and not the increase in the greenhouse gas concentrations (although global climate change patterns forced by GHGs can include atmospheric circulation changes).

The key factor is that the ozone hole above the South Pole has changed the wind patterns – when ozone is removed from the stratosphere, less solar UV radiation is absorbed so the polar stratosphere cools. This increases the temperature change as you move away from the pole and, in turn, has changed the westerly (clockwise) winds that circle the pole – they are now further south and faster.

This wind pattern spreads down through the atmosphere towards the planet’s surface and has, therefore, brought more warm air from over the Southern Ocean to the Peninsula. This circulation change has less effect on the Antarctic interior and possibly even isolates it from the rest of the Earth system.

This climate change pattern is really interesting to study and we can even use ice core data from the Antarctic to look at how these winds have changed in the past – I’ve recently reviewed the literature on this subject (Russell and McGregor 2010).

Korhonen et al. (2010) have even found another mechanism of how these wind changes have affected the climate. As the wind speed over the ocean increases, it throws up more spray and this means that more clouds can form over the Southern Ocean and Antarctica (I’ll write a post later about how clouds form). If there are more, bright clouds around then these reflect away more incoming sunlight, which will cool the region beneath these clouds.

So, to bring all this together, if the Antarctic continent has been cooling (which isn’t clear) then this could be because the normal rules don’t apply to Antarctica. Does this mean that we can say that Antarctic climate change is the exception that proves the rule of GHG forced climate change?

Probably not, but it does highlight just how complicated the climate system is and how much more there is find out about it!

References:

Korhonen, H., Carslaw, K., Forster, P., Mikkonen, S., Gordon, N., & Kokkola, H. (2010). Aerosol climate feedback due to decadal increases in Southern Hemisphere wind speeds Geophysical Research Letters, 37 (2) DOI: 10.1029/2009GL041320

Russell, A., & McGregor, G. (2009). Southern hemisphere atmospheric circulation: impacts on Antarctic climate and reconstructions from Antarctic ice core data Climatic Change DOI: 10.1007/s10584-009-9673-4

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On “the real holes in climate science”

[This post is based on a question I got in response to a previous post but thought it deserved a short post on its own as there’s a few interesting points.]

There’s been a lot of bad press recently for climate science but a lot of has focused on very minor issues. For example, most of the coverage on the UEA CRU email leak/theft/hack (so-called climategate) has focused on what some of the “skeptic” community wished was in the emails rather than what was really there. The Guardian has gone over some of the issues from the leak in depth in a recent series of articles, although this seems like a lot of focus on old issues. As Prof. Phil Jones himself said in a recent interview in The Sunday Times: “I wish people would read my scientific papers rather than my emails”. Glaciergate was equally blown out of all proportion given that the original claim only appeared in one sentence in a 3000 page report.

In the midst of all this, Nature printed a nice feature looking at the real big gaps in climate science (Schiermeier 2010), but it is behind a paywall, which is a shame because it’s a good piece. So, I thought I’d provide a very quick summary here.

Regional climate prediction

We still don’t have sufficient computing power to run models at high enough resolution to make projections on the scale that would be useful to policy makers. This is clearly required to make big infrastructure decisions.

Precipitation

Projections of precipitation patterns are really hard to make as they depend on temperature changes, circulation changes, radiative balance changes and pollution (and, therefore, cloud condensation nuclei) changes. Yet precipitation changes will probably have the biggest impact on society.

Aerosols

The effect of aerosols (i.e. small solid particles or liquid droplets suspended in the atmosphere) is a big unknown. Different types do different things and its not really certain whether they have a generally cooling effect – by reflecting away solar radiation – or a warming effect – by promoting more cloud growth and trapping more terrestrial heat. That said, any cooling effect would be very unlikely to reverse the warming impact of greenhouse gases.

The tree-ring controversy

This relates mostly to the “hockey stick” graph and the reliability of the palaeoclimate data we use to put our current climate into perspective. It’s important that we learn from past climate changes as we only have one atmosphere and can’t do experiments with it. But it is not easy to get palaeoclimate data (tree rings, ice cores, sediment cores) or to interpret them properly.

So what is the “consensus”?

In a certain sense, when people talk about the “scientific consensus about climate change” they really mean little more than our understanding of the greenhouse effect, our impact on it and that things are very likely to get messy in the future. All the details are still very much under investigation.

Reference:

Schiermeier, Q. (2010). The real holes in climate science Nature, 463 (7279), 284-287 DOI: 10.1038/463284a

1 REASON WHY CLIMATE CHANGE IS MAN MADE

The front cover of yesterday’s Daily Express is shown below.  Oh dear.  As an atmospheric scientist, I reckon I could come up with more than 100 real scientific reasons why Earth’s climate changes naturally.  However, the Express article is more political than scientific and it doesn’t really reflect the headline.

Unfortunately, even if they had listed 1000 reasons why our climate changes naturally, it still wouldn’t undermine the 1 reason why most of the recent climate changes have happened because of our activities:

We have emitted millions of tonnes of greenhouse gases over many years.  These gases block outgoing heat from the planet.  We have evidence of “unnatural” climate changes in the recent past and fully expect much more in the future.  This point is not refuted by any of the 100 points given in the Express article.

Where to start on climate change?

Climate change usually only comes up in the media and online when there is some progress on a small detail or when something like Copenhagen or the UEA email theft happens.  I think that this presents a big problem as the people consuming these stories might not know the basic science yet, these days, everyone is expected to have an opinion on climate change.  This issue is amplified on the web where George Monbiot’s column on the Guardian website, for example, regularly receives more than 1000, usually anonymous and often controversial, comments.

So I thought it might be a good idea to write a quick blog post for a complete climate science beginner. I’m only going to tackle two questions here, skipping over quite a lot of things, but they are the key points to understanding climate change.

What are greenhouse gases and what to they do?

All our planet’s energy comes from the Sun.  Most of the radiation from the Sun goes straight through our atmosphere.  When Earth absorbs the Sun’s radiation the planet heats up and then re-emits a slightly different type of radiation.  The atmosphere can absorb this different type of radiation.  This keeps some of the heat near the Earth like a blanket, or a greenhouse.  The greenhouse effect is really important because without it the Earth would be much colder and our lives would be very, very difficult.  Most of this science was known by about 1850 – we’ve been working on the details since then.

How has the concentration of greenhouse gases changed?

Ironically, also by about 1850, the Industrial Revolution had really got going and people were beginning to burn lots of fossil fuels and change the make up of our atmosphere.  In particular, carbon dioxide was being released in great quantities.  Our best measurements of CO2, however, didn’t start until the 1950s in Hawaii (see graph).  This shows a really clear increase in atmospheric CO2.  This increase is having an affect on global temperatures because the greenhouse effect is keeping more heat in than it used to.

This is the climate change problem described in its most basic form – more greenhouse gases lead to a change in the energy that is retained from the Sun.  How this affects the Earth, though, is quite complicated (this why we talk about “climate change” more than “global warming” now) but the basic idea is quite simple.

Still want to know more?

If you still want to know more then I would say that the best place to start, as far as reliability and lack of agenda is concerned, would be the Intergovernmental Panel on Climate Change – this is a scientific group, organised by the UN, who review all the science relevant to climate change.  This is obviously a massive task but, nonetheless, they publish their reports in full online – the last science report came in at around 1000 pages long.  This is clearly not very easy to get to grips with.  However, the do produce a short and well written Summary for Policymakers that covers most of the big issues.  Also, they produce a Glossary where you can find the meanings of any terms you don’t understand.  I really hope that more people go and find out more about the interesting science behind our planet’s weather and climate!