Earth Not Cooling; Global Warming Still Happening

Apparently some climate change skeptics are using the relatively mild summer experienced by some parts of the US to push the notion that global warming has stopped and the earth is cooling. In their eyes, of course, this means there is no need for restrictions on carbon emissions or new efficiency standards. It would be comforting if this were the case, but the evidence does not support it.

According to data from the National Space Science and Technology Center in Huntsville, Ala., the global high temperature in 1998 was 0.76 degrees Celsius (1.37 degrees Fahrenheit) above the average for the previous 20 years.

So far this year, the high has been 0.42 degrees Celsius (0.76 degrees Fahrenheit), above the 20-year average, clearly cooler than before.

However, scientists say the skeptics' argument is misleading.

"It's entirely possible to have a period as long as a decade or two of cooling superimposed on the long-term warming trend," said David Easterling, chief of scientific services at NOAA's National Climatic Data Center in Asheville, N.C.

"These short term fluctuations are statistically insignificant (and) entirely due to natural internal variability," Easterling said in an essay published in the journal Geophysical Research Letters in April. "It's easy to 'cherry pick' a period to reinforce a point of view."

Climate experts say the 1998 record was partly caused by El Nino, a periodic warming of tropical Pacific Ocean waters that affects the climate worldwide.

Indeed, El Nino has returned this year, and already we are starting to see some record or near-record temperatures. Global ocean surface temperatures were the hottest on record in June and in July. This year has also featured the second hottest global mean temperature for July. Clearly some of this is being caused by El Nino, just like the record temperatures of 1998, but it seems premature to declare that we are entering a global cooling phase at the same time as the oceans are hitting record temperatures.

The cooling argument largely rests on isolating the years since 1998, as in the following graph from the McClatchy article linked above:

It is true that global average temperatures have failed to match those of 1998 in the years since. In fact, they have generally stayed at least three tenths of a degree below the 1998 average high. Yet even within this cherry-picked decade, there appears to be a subtle upward trend, if one ignores the extreme high of 1998 and the extreme lows of 2000 and 2008, and several of those years rank just below 1998 on a list of hottest years.

If you extend the timeline back further, as in the graph above from FiveThirtyEight, the temperatures from the past decade do not seem like evidence of cooling. Instead they seem right in line with the long term warming trend.