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Yes, the planet has kept warming since 1998

By Joe Romm  

"Yes, the planet has kept warming since 1998"

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UK Met Office Hadley Centre datasetAs part of their climate myth series, New Scientist cuts through the nonsense on what’s happened globally in the last decade:

In fact, the planet as a whole has warmed since 1998, even in the years when surface temperatures have fallen.

According to the dataset of the UK Met Office Hadley Centre (see figure), 1998 was the warmest year by far since records began, but since 2003 there has been slight cooling.

NASA's global temperature land-ocean indexBut according to the dataset of NASA’s Goddard Institute for Space Studies (see figure), 2005 was the warmest since records began, with 1998 and 2007 tied in second place.

The difference between the two datasets goes to the core of why the planet has in fact been warming since 1998:

The main reason is that there are no permanent weather stations in the Arctic Ocean, the place on Earth that has been warming fastest. The Hadley record simply excludes this area, whereas the NASA version assumes its surface temperature is the same as that of the nearest land-based stations.

It is possible that the NASA approach underestimates the rate of warming in the Arctic Ocean, but for the sake of argument let’s assume that the Hadley record is the most accurate reflection of changes in global surface temperatures. Doesn’t it show that the world has cooled since the record warmth of 1998, as many claim?

Not necessarily. The Hadley record is based only on surface temperatures, so it reflects only what’s happening to the very thin layer where air meets the land and sea.

In the long term, what matters is how much heat is gained or lost by the entire planet – what climate scientists call the “top of the atmosphere” radiation budget – and falling surface temperatures do not prove that the entire planet is losing heat.

… the planet is gaining as much heat from the sun as usual but losing less heat every year as greenhouse gas levels rise (apart from the exceptional periods after major volcanic eruptions, such as El Chichon in 1982 and Pinatubo in 1991).

How do we know? Because the oceans are getting warmer.

Tricky oceans

Water stores an immense amount of heat compared with air. It takes more than 1000 times as much energy to heat a cubic metre of water by 1 degree Centigrade as it does the same volume of air. Since the 1960s, over 90% of the excess heat due to higher greenhouse gas levels has gone into the oceans, and just 3% into warming the atmosphere (see figure 5.4 in the IPCC report (PDF)).

Globally, this means that if the oceans soak up a bit more heat energy than normal, surface air temperatures can fall even though the total heat content of the planet is rising. Conversely, if the oceans soak up less heat than usual, surface temperatures will rise rapidly.

This is why surface temperatures do not necessarily rise steadily year after year, even though the planet as a whole is heating up a bit more every year. Most of the year-to-year variability in surface temperatures is due to heat sloshing back and forth between the oceans and atmosphere, rather than to the planet as a whole gaining or losing heat.

The record warmth of 1998 was not due to a sudden spurt in global warming but to a very strong El Nino (see figure, right). In normal years, trade winds keep hot water piled up on the western side of the tropical Pacific.

During an El Nino, the winds weaken and the hot water spreads out across the Pacific in a shallow layer, which increases heat transfer to the atmosphere. (During a La Nina, by contrast, as occurred during the early part of 2008, the process is reversed and upwelling cold water in the eastern Pacific soaks up heat from the atmosphere.)

A temporary fall in the heat content of the oceans at this time may have been due to the extra strong El Nino.

What next?

Since 1999, however, the heat content of the oceans has steadily increased again (despite claims to the contrary). Global warming has certainly not stopped, even if average surface temperatures really have fallen slightly as the Hadley figures suggest.

If you want to know what’s coming next, read “Climate forecast: Hot and then even hotter.”

Here are all of the myths New Scientist takes on:

Can we trust the science?

Chaotic systems are not predictable
We can’t trust computer models of climate
Many leading scientists question climate change
It’s all a conspiracy
They predicted global cooling in the 1970s

Is the sun to blame?

Global warming is down to the Sun, not humans
It’s all down to cosmic rays

Does CO2 cause warming?

Human CO2 emissions are too tiny to matter
CO2 isn’t the most important greenhouse gas
Ice cores show CO2 increases lag behind temperature rises, disproving the link to global warming
Ice cores show CO2 rising as temperatures fell
The cooling after 1940 shows CO2 does not cause warming

What happened in the past?

The ‘hockey stick’ graph has been proven wrong
It’s been far warmer in the past, what’s the big deal?
It was warmer during the Medieval period, with vineyards in England
We are simply recovering from the Little Ice Age

What is happening now?

Mars and Pluto are warming too
Antarctica is getting cooler, not warmer, disproving global warming
Polar bear numbers are increasing
The lower atmosphere is cooling, not warming
The oceans are cooling
Global warming stopped in 1998

What is going to happen?

Warming will cause an ice age in Europe
Higher CO2 levels will boost plant growth and food production
Hurricane Katrina was caused by global warming

Why should I worry?

It’s too cold where I live – warming will be great
We can’t do anything about climate change

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10 Responses to Yes, the planet has kept warming since 1998

  1. paulm says:

    Good post, great links.

  2. rpauli says:

    As I look at your 3 charts – I see a slope beginning around 1910.

  3. David B. Benson says:

    rpauli — From the physics, we know that the upward tend began about 1750 CE with the industrial revolution. Its just hard to pick out of the natrual climate variability until about 1980 CE.

  4. Uosdwis says:

    The deniers will probably jump all over a BBC Science headline “World heading toward cooler 2008.” They say it’s just a brief pause caused by La Nina, but still will be one of the 10 warmest years since 1850. But, like I said, they’ll just see the headline and scream “See? Global warming is over!”

  5. JamesG says:

    They’ve only actually made a case that the Arctic is warming while the rest of the planet isn’t. This is based on extrapolation ie guesswork but nevertheless since the Arctic is a very small area of the globe, do none of you question why it seems to have such a disproportionate effect on GISS global temperatures? Hadley rightly assumed that skipping the Arctic temps shouldn’t make that much difference. And indeed it shouldn’t. To get such an effect, your extrapolated temperature must be really huge indeed. The other oddity about GISS is that they have the lowest 1998 peak of all the temperature records. The effect is to promote 2005. And how many of you guys knew that 2005 was also a very strong el niño year? As indeed was the start of 2007 which also gave a false peak in GISS but not in any of the other records. So this extrapolation procedure gives a low 1998, a high 2005 and a higher 2008 than all the other records. And none of you are suspicious! The IPCC prefers Hadley’s chart – they likely don’t trust Hansen’s extrapolations either.

  6. “Very small area”?

    According to my quick reality check, at 14 million square kilometres the Arctic Ocean is 10 per cent of the size of the Pacific Ocean, makes up more than 4 per of the total ocean area and nearly 3 per cent of the planet’s total surface area.

    Yup, very small.

    Nice site, btw.

  7. Peter Holubz IV says:

    Tim Patterson, a paleoclimatologist from the department of Earth sciences, will give an opposing view to Al Gore’s An Inconvenient Truth. Patterson is speaking at a Canadian Club of London luncheon.

    He believes we should expect global cooling rather than global warming in the coming years.

    “We’re off on the wrong foot,” he says. “There’s been no global warming in the 21st century.”

    Climate change is not caused by humans, but by natural forces, Patterson says.

    http://lfpress.ca/newsstand/News/Local/2008/11/17/7433876-sun.html

  8. Sam Eagle says:

    What would be the ideal temperature to set the Earth’s thermostat to, if you could?

  9. shop says:

    It is possible that the NASA approach underestimates the rate of warming in the Arctic Ocean, but for the sake of argument let’s assume that the Hadley record is the most accurate reflection of changes in global surface temperatures. Doesn’t it show that the world has cooled since the record warmth of 1998, as many claim?

    Not necessarily. The Hadley record is based only on surface temperatures, so it reflects only what’s happening to the very thin layer where air meets the land and sea.

    In the long term, what matters is how much heat is gained or lost by the entire planet – what climate scientists call the “top of the atmosphere” radiation budget – and falling surface temperatures do not prove that the entire planet is losing heat.