Tuesday 7th April 12:53 pm
Global warming ‘pause’ explained
Tuesday 16th September 2014 12:16 pm
In general, scientists are a pretty mild and inoffensive bunch. But over the last decade, one specific group of scientists has come in for a lot of criticism. So let’s dive into the topic of ‘the pause in global warming’.
In the USA, the Wall Street Journal wrote, “temperatures have been flat for 15 years – nobody can properly explain it.”
Another newspaper from the same stable, the UK Daily Mail wrote “global warming ‘pause’ may last 20 more years, and Arctic sea ice has already started to recover”. Both of these statements are very reassuring, but unfortunately, very very wrong.
With regard to this ‘pause’, there are two major claims made by those who deny the science of climate change.
The first one is that the climate is actually cooling – not warming. This is incorrect.
The second claim is that after some previous warming, the global climate is now constant, and neither warming nor cooling. In other words, that the climate is in a kind of holding pattern, or haitus. This is also incorrect.
So let’s look at the claim that the surface temperatures have not increased since 1998.
But first, why the year 1998? Why not 1997, or 1999?
It turns out that the year 1998 was a very, very hot year. It took until 2005, and then 2010, until we had hotter years. The year 1998 was very hot due to a few factors. The major factor was that 1998 was the most severe example of an El Niño year for over a century.
In the Pacific Ocean, there is a repeating pattern of El Niño events and La Niña events. El Niño years are hotter, and here the Pacific Ocean releases its heat to the atmosphere.
On the other hand, La Niña events are cooler, and here the Pacific Ocean sucks heat from the atmosphere.
You can see how this could affect the global climate, especially when you consider that by itself, the Pacific Ocean is bigger than all the land masses on Earth added together.
Let me get back to 1998. In that severe El Niño year, the Pacific Ocean dumped about 42 zetajoules of energy into the atmosphere. (By the way, “zeta” means “1” followed by 21 zeros, so it’s a really big number).
To put that into perspective, each year, the human race generates about half-a-zetajoule of energy in its power stations. The amount of heat energy that the Pacific Ocean released into the atmosphere in 1998 was about 80 times more than the energy generated by the human race in that calendar year of 1998.
So for a while, 1998 topped the charts for the hottest year on record.
We then had record-breaking heat waves in Europe in 2003. In 2010, the hottest year so far, the record-breaking summer heat and fires were responsible for the deaths of 50,000 people in Russia.
This was followed by record-breaking heat waves in the USA in July 2012, and in Australia in January 2013. Globally, in 2014, we had the hottest May and June ever on record, and the equal-warmest April. And let’s not forget that 13 of the 14 warmest years on record have happened in the 21st-century.
Let me also point out that the hottest years on record ever, 2005 and 2010, happened during a La Niña-dominated period – when you would expect cooling.
So it’s very wrong to claim that surface temperatures are cooling. It’s also very wrong to claim that surface temperatures are constant. The climate is still heating up.
What is causing this heating? Various greenhouse gases such as carbon dioxide, methane and nitrous oxide trap the incoming energy from the Sun. The greenhouse gases let the Sun’s energy enter the atmosphere, but stop some of it from leaving. The amount of extra heat trapped in the atmosphere by these greenhouse gases is equal to the energy released by some 400,000 Hiroshima atom bombs each day.
The current carbon dioxide levels are about 40% higher than they were in the 19th century. They are also at their highest levels for the last 800,000 years. Indeed, over the last 800,000 years, carbon dioxide levels stayed within the range of 170 – 280 ppm until the Industrial Revolution.
That makes the sudden recent jump to 400 ppm over the last two centuries really quite astonishing. In fact, in the year 2013, the carbon dioxide levels grew at the fastest rate ever measured since reliable global records began.
So why all the talk about the pause in climate warming? It turns out that if you try really hard to mangle the data, and cherry pick very skillfully, you can make a case — and I’ll put that side of the argument together, next time…
This blog first appeared on Dr Karl's Great Moments in Science
© 2017 Karl S. Kruszelnicki Pty Ltd