Has global warming stopped?

Andrew Pendleton

26 June 2012

During my appearance on the BBC's Daily Politics programme last week, host Andrew Neil asked whether global warming (presumably the increase in global average land surface temperature) had stopped - and asked me to write a blog about it.

As I made clear on the programme, I'm not a climate scientist. So I consulted some climate scientists and scientific literature from respected institutions - which I'd also read before going on the programme - in writing this piece.

Below is a very helpful graph that combines four of the world's most authoritative data sets on global, average surface temperature: two from the US, one from the UK and one from Japan.

The data in the graph is important for three reasons. First, it shows a long term warming trend - and quite a dramatic one - beginning in the early 20^th Century and, evidently, still underway. Second, it shows how four separate data sets reach broadly the same conclusion. And third, it shows how much fluctuation there is from year-to-year and, in fact, from decade-decade.

As Chris Rapley, Professor of climate science at UCL put it to me "No climate scientist ever stated or expected the global average temperature to rise as a smooth curve. If you look back over the data for the last 100 years rather than just cherry-picking a short [in climate terms] period, the fluctuations are very clearly evident. But so is the upward trend, especially of the last 40 years."

Related to this and having seen last Friday's Daily Politics, Bob Ward at the London School of Economics sent me some very useful, basic number crunching from the team at the Grantham Research Institute on Climate Change and the Environment. The table in the blog shows in statistical terms what the graph above illustrates what Prof. Rapley says: warming accelerates and slows, but the long-term trend is clearly upwards.

A further complicating factor is that while the long-term trend is clear, part of the explanation for the fluctuations over the short term is that the energy from the sun is stored in different places - the land, the oceans and the atmosphere.

This energy - which is increasing in overall volume due to the enhanced greenhouse effect caused by human emissions of carbon dioxide and other gases - may not show up as increased surface temperature. Instead it may be transferred into warming of the ocean's interior where it is hidden from the surface temperature data, the melting of ice caps, or accelerated movement of oceans or atmosphere.

A very good explanation of why we should in fact focus broadly on the growing energy imbalance (i.e. too much of the sun's energy being trapped inside the atmosphere) due to a higher concentration of greenhouse gases rather than narrowly on temperature is contained in this blog.

In a nutshell the simple answer to the question posed on the programme and to the challenge by Andrew Neil is 'no, global warming has not stopped.'

This is why Friends of the Earth is campaigning for more efficient use of energy across our economy and for a major shift to the harnessing of energy from the sun, sea and wind to reduce emissions of carbon dioxide.

While climate change is Friends of the Earth's main reason for campaigning for renewable and efficient energy, there are many other very sound reasons for investing in renewable energy sources too.

For instance, we have an abundance of natural renewable energy sources in and around the UK and more efficient use of energy will save us and our economy money. See our Clean British Energy campaign for more details.

In particular, what we're calling for in the campaign is for the energy bill's primary purpose to be the virtual elimination of carbon emissions from electricity generation by 2030. The massive opportunity for the UK is that a shift to renewables, though requiring investment upfront, promises permanent release from high and increasingly expensive future fossil fuel imports in favour of free fuel from the wind, sea and sun.