There is a difference between weather and climate. Weather is what you see when you look out of the window; climate is the pattern that remains when day-to-day variations are set aside and the long-term average is considered. Weather is about events; climate is about trends. Climate is what we expect to see; weather is what we actually get.
The Met Office's revised predictions on medium-term climate change released this week have been seized upon by sceptics who insist that man-made global warming caused by excess CO2 in the atmosphere is an invention of over-zealous environmentalists. Global warming is "at a standstill", headlines have crowed, and the danger posed by greenhouse gases is more seriously questioned than ever. If only it were so simple.
What the Met Office's latest computer model actually says is that the global temperature may rise at a fractionally shallower rate over the coming five years than had been predicted. But we can still expect more above-average warmth than the world has experienced in the previous 50 years. Climate change is, then, no less of a grim reality than it was and there is no reason to conclude that it has "stalled".
What is important here is distinguishing the natural variability of the Earth's climate – an inherently chaotic system – with the man-made warming caused by greenhouse gases.
Natural rhythms in the Earth's weather have many causes, including volcanic eruptions, oceanic currents and the 11-year solar cycle. In El Niño years, for example, warm water spreads out across the equatorial Pacific and heat leaves the ocean for the atmosphere, while at other times the seas absorb more heat from the atmosphere. In fact, the phenomenon is thought to have played a role in last year's dramatic melting of the Arctic sea ice, which occurred despite summer air temperatures that were not particularly high.
To conclude from the Met Office data that man-made global warming need no longer concern us is, then, a misunderstanding of both the figures themselves and the nature of the climate. Meteorologists are only beginning to understand the complex interactions between the elements of the Earth's various natural cycles. But what is now clear is that rhythms which cover a few years can mask longer-term trends. Thanks to their natural cycles, the oceans – which one climate scientist has described as the sleeping giant of climate change – have acted as a vast heat store. Indeed, as much as 90 per cent of the heat generated from accumulating greenhouse gases has been absorbed by the oceans. And the latest Met Office modelling suggests that this phase will continue for the coming four or five years, leaving global average air temperatures only a little hotter while the warming from greenhouse gas emissions nonetheless continues.
At the end of the decade, though, the oceanic cycles may change. At which point, the seas might start to release heat, instead of soaking it up, perhaps provoking another sharp rise in global temperatures. The underlying problem will not have changed, but the ocean's absorption will no longer be masking it.
There is much uncertainty here. Scientists' understanding of the mechanisms of and influences on the Earth's natural rhythms is still inexact. Measurements of the underlying problem of climate change are frighteningly clear, however. They can be neither ignored, nor denied. The comfort blanket of the climate sceptics is a delusion. And the need for global action on climate change is as desperately urgent as ever.Reuse content