‘How can we be sure global warming isn’t part of a natural cycle?” a colleague asked at lunchtime recently. “Climate has always changed – look at the ice ages!”
It’s a fair question. One answer is that most scientists who specialise in the study of past climates are pretty sure the current warming is man-made. However, simply deferring to expert opinion doesn’t really answer the question.
A better answer is that natural factors known to have affected global climate in the past don't seem to correlate well with the recent warming. Extensive studies of changes in the sun's energy, perturbations in the Earth's orbit, cosmic rays and other phenomena have failed to reveal a pattern that correlates with the warming measured over the past century. On the other hand, the Earth's climate is known to be very sensitive to certain greenhouse gases in the atmosphere, and a steady rise has been observed in the concentration of these gases that correlates uncannily well with the warming. Other evidence, such as satellite measurements of changes in the energy escaping from Earth into space, and a detected cooling of the stratosphere, make it extremely likely that the source of the warming lies close to home.
This second answer also has its problems – before long the discussion has become very technical. My colleague says he feels a bit like a tourist who has asked for directions in school French and has been answered in strong dialect.
“So why not trust the experts?” a mathematics lecturer asks. “After all, we trust them on the dangers of tobacco, childhood obesity and so on. Why not on climate change?” Perhaps it is because most people don’t imagine they know much about lung cancer or cardiovascular fitness, while we are all familiar with climate. Or we think we are.
The problem is that what we experience is weather, not climate. While weather varies in quite a chaotic way from day to day and from place to place, climate is the statistical average of long-term weather patterns over very large regions. Climate varies surprisingly little over time; thus one can predict with confidence that summer will be hotter than winter in Arizona in 2020, while the weather in London next week is much less certain.
So perhaps our natural experience of weather conspires against our understanding of climate. Meanwhile, the boffins painstakingly extract climate data from the statistics of countless weather measurements worldwide and have discovered a small but systematic warming trend can be observed in global climate..
“But didn’t I read somewhere that global warming has stopped?” my first colleague asks.
Certainly, the increase in surface temperatures over land and sea has slowed somewhat in the past decade. However, global climate is a complex system and the warming is observable in other ways such as a steady rise in ocean temperatures, a rise in sea level and a melting of polar ice. It seems that global warming is well under way, a phenomenon that could have devastating consequences for many regions of the world.
“So what’s the solution?” the mathematics lecturer asks.
There is much debate on the best way to slow the warming, from imposing limits on greenhouse gas emissions from fossil fuels to increasing energy efficiency. However, achieving international agreement on the matter is very difficult, as individual nations do not want to disadvantage their economies by imposing carbon targets. Developing countries seek to industrialise just as developed nations did many years ago, while the latter fear economic contraction if they forgo fossil fuels too quickly.
The biggest problem is that there is no real political consensus on the need for action. One reason for this is that a great many conservative politicians worldwide simply do not accept the scientific evidence for man-made warming (presumably because the prospect of governmental action conflicts with the principles of the free market). This rejection of well-established science due to political ideology is extremely worrying, as inaction will almost certainly lead to an acceleration in global warming. A related problem is that media outlets controlled by conservative interests also tend to dismiss or downplay the problem. This influences public opinion, making it difficult for democratic states to take action.
Dr Cormac O'Raifeartaigh lectures in physics at Waterford Institute of Technology and writes the blog Antimatter