“A gentle warming of up to about 0.5 deg. C occurred between 1979 and 1998; but since 1998 global temperature has now been static or cooling gently for ten years, despite continuing increases in CO2 emissions.”
—Bob Carter, geologist specializing in palaeontology, stratigraphy, marine geology, and environmental science
I’m not sure how often you hear this sort of claim, but I get comments like this a lot. Many people who respond to this blog who aren’t convinced about global warming and climate change will refer to this “fact.”
But is it a fact? Many people point to the longer trends rather than just the span of less than fifteen years to refute claims that global warming has stopped. A popular reference being used is the escalator to the right which shows that depending on where you start and stop, you can refer to many periods where the trend in temperature seemed to remain static or even drop over shorter time spans. This simply underscores the importance of looking to a longer trend to know what’s really happening to surface temperatures.
But there’s more to it than that. One of the reasons the year 1998 is centred out is because that year was the hottest on record to that point. (Since then, 2005 became the hottest year, tied again by 2010. 2012 is looking to possibly break the record further.) And the reason 1998 was such a record-breaker was because it was affected by an unusually strong El Nino, with a substantial transfer of heat from the Pacific Ocean into the atmosphere. Subsequent years were cooler due to the La Nina conditions which followed.
But surface temperatures aren’t the only way to assess for global warming, because land surfaces aren’t the only part of this planet. There’s also atmosphere, water, and ice, all of which are affected by global warming. The best way to think about global warming is to consider the added heat content to the planet as a whole, and not just one component of it.
Temperatures on both land and in the atmosphere have been increasing over the long term, but there are many variables such as El Nino that can also have an impact, making those signals particularly noisy. But a noisy signal is certainly not enough to hang your hat on if you want to argue that global warming stopped more than a dozen years ago.
We’ve seen evidence that the other components of our planet are also being affected by added heat content. In fact, the oceans have also been warming and have been absorbing more of the heat energy than the air and land surfaces have been. This information has been demonstrated by D.M Murphy from the NOAA in a paper published in 2009.
And of course, many sources of ice on our planet are melting. We’ve seen many examples over the last few years of melting glaciers, melting ice at Greenland, and a shrinking ice cap at the North Pole. As ice melts, heat energy is used to change the phase of water from solid to liquid. The phase transition doesn’t lead to any actual warming, not until the melting is completed and the energy is heating the liquid water. But it’s still part of the bigger picture of global warming, added heat content to our planet, melting more ice than we’ve seen in previous years.
So with gradual rises—albeit with noisy signals—in both surface temperatures and tropospheric temperatures, with warming oceans, and with melting ice, all components of our planet are showing effects from global warming. For those who want to stay focussed on the noise in the signal of one small part of it, all I can suggest is that they’re missing the much bigger picture.
And that raises the question: do they focus on land and air because that’s where we live out the majority of our lives, missing the oceans and ice masses due to an out-of-sight-out-of-mind phenomenon? Or is there a motivating factor to believe that global warming isn’t real.