One of the arguments currently popular with climate change contrarians and science deniers is that climate change has paused, or, in less moderate language, global warming stopped in 1997. Either phrasing is wrong, but there’s wrong, and then there’s climate denier wrong, and we didn’t realise quite how spectacularly wrong this was until this week.
Firstly, be wary of statements made about the climate using short data-sets. Thirty years is accepted in the field as the standard period over which a climatic change can be observed. Changes over shorter periods may be confirmed as climatic change as more data comes in, but trying to work out what’s going on from a data set covering less than thirty years means you might be mistaking weather for climate. Often, the signal is strong enough for confident assertions to be made about periods of twenty to twenty five years, but not, as a rule, for periods shorter than that.
Secondly, watch out for cherry-picking. All the climate deniers who want to claim that climate change has stopped take 1997, and sometimes the autumn of that year, as the starting point for their data set. Why would you choose autumn 1997, instead of, say, January 2000 (too recent, but a nice round number), or 1950 (the climate scientist’s usual proxy date for ‘the present’), or 1983 (thirty years ago – giving the most recent data set which might be regarded as a reliable guide to what was happening to the climate now)?
Because starting your data set at any of those times gives a strong warming trend.
But 1997 was an outlier - that is, due largely to a strong El Nino effect 1997 was an abnormally warm year. If you want to know what the climate is doing, 1997 is a bit of very loud noise which makes the underlying signal harder to trace. But if you want to manipulate the data to show a pause in warming, then 1997 is the holy grail of data points. You can start your dataset there, at a freak temperature high, and present that freak result as a baseline to measure subsequent years against. Unsurprisingly, most of the years immediately following your outlier will be closer to the mean – that’s what ‘outlier’ means. Starting a data set with an outlier will generally lead to confusing results, particularly when your data set is too small anyway.
Thirdly, even using the deniers’ favoured time period, and their favoured measurement, surface temperature, the world has still warmed since 1997. Both 2005 and 2010 were warmer than 1997, and the outlier high temperatures of 1997 are now the average. However, this warming isn’t ‘statistically significant’ (a technical term which means ‘statisticians are 95% confident that the trend revealed in the data is a real trend and not just random noise’) due mainly to the short data set which prevents confident statements being made about it. So if you want to be rigorous about it then the data set for that period proves nothing. But if you’re happy using statistically inadequate data sets, as the deniers seem to be, well, their data set shows warming.
However, it doesn’t show very much warming, and this is the interesting question hidden in the deniers’ bluster. Is there a reason why the rate of warming in the last fifteen years appears to be slower than the rate of warming prior to that?
Well, there’s a two-stage answer to that question.
If you take thirty-year periods, rather than fifteen year periods, there is no change in the surface temperature warming trend, so the slow-down is just a statistical artefact created by cherry-picking your starting year. However, even a continuation of the unprecedented rate of warming in the eighties and nineties doesn’t quite match with the forecasts – according to the science, we should be seeing accelerating warming.
And now, unfortunately, we are. New research shows that the Earth is actually heating up at an accelerating rate, but the heat is not being equally distributed. For the last decade, weather and wind conditions primarily caused by the Decadal Pacific Oscillation (that’s El Nino/La Nina again) have entailed more of the extra heat ending up in the deep ocean. Theoceans absorb 90% of the extra heat in our warming world, and so surface temperatures, the obvious measure to a surface-dwelling species like us, aren’t the anywhere near the whole story. As it turns out, 30% of the additional heat is 700m deep below the waves. That sounds like good news – surely we’re better off storing the heat out of the way in the depths rather than confronting it where we live? But it isn’t. Thermal expansion is the main force driving sea-level rise, so more heat in the oceans means a faster rise and more flooding. Warmer oceans also threaten faster sea-ice melt, stronger hurricanes and disrupted oceanic currents. And that’s if the heat stays where it’s put, which, of course, it won’t – there is constant transfer of heat between atmosphere and ocean, on a mammoth scale, in fact that’s what El Nino/La Nina is.
The Earth isn’t cooling, global warming has neither stopped nor slowed down, and whilst claiming otherwise might sound more reasonable than the traditional denier conspiracy theories, it’s just as wrong, and often it’s the same people making those claims.
Nor has warming continued at the same rate as in the last century. The world is warming faster than at any time in the last 10,000 years, and that rate of warming is accelerating.
So, is it time to panic yet? If we take responsibility for our world and our children’s futures, do what we can to reduce our personal carbon emissions, send a signal to the markets that we’re ready for the low carbon economy, and, more importantly, send a much more explicit message to our politicians that we want leaders with solutions, not roadblocks to progress, then we can still pull the iron out of the fire and save most of what makes this planet so uniquely spectacular. Not to mention inhabitable.
But if we’re passively waiting for the government to sort it out, then yes, we’re doomed.