New research suggests global warming is accelerating

As humans emit more greenhouse gases like carbon dioxide into the atmosphere, the Earth continues to warm. When I use the term “warm”, I mean there is an increase in thermal energy (heat) contained in the oceans and atmosphere of this planet.

We can measure warming by measuring temperatures; however, obtaining an accurate reading of the Earth’s temperature is complicated. Temperatures change with seasons, with locations, and there are natural long term variations that move heat around. So, we don’t expect temperatures just to continue increasing at all locations and at all times. We do expect the long term trend to be upwards, however, and that is what we’ve observed.

But if you follow the conversation about global warming, and particularly if you listen to cable news or online bloggers, you might have heard that there has been a hiatus or a halt to global warming. I’ve written before on this site that there is no halt, there never has been one. However there has been a vigorous debate about whether the increase in lower atmosphere temperatures has slowed down.

A new paper, “Possible artifacts of data biases in the recent global surface warming hiatus” just published today in Science deals with this issue. In particular, the lead researcher Dr. Thomas Karl and his colleagues investigate the quality of the near-surface temperature records and ask whether they really show a slowdown.

The scientists make a number of improvements upon existing information. First, they focus on ocean surface temperature measurements from floating buoys and from ship-board sensors. We know that temperatures measured by ship sensors are often warmer than temperatures measured by buoys, in part because of the heat generated by the ship engine. A more thorough accounting of this effect has been implemented in the Extended Reconstructed Sea Surface Temperature data set version 4. This accounting is utilized in the paper.

Second, there has been a historical change in how ships measure surface temperatures. Decades ago, temperatures were mainly measured by insulated buckets. Around the time of World War 2, there was a change from insulated buckets to temperature sensors contained within ship hulls. The ship hull sensors recorded warmer water temperatures compared to the bucket method. A more thorough handling of the changes from buckets to ship hull sensors was also included in the new paper.

Finally, the new study used more recent estimates of the land temperatures. The new estimates combine multiple temperature databases into a single integrated whole.

The end result is that the temperature trends over the past 17 or so years has continued to increase with no halt. In fact, it has increased at approximately the same rate as it had for the prior five decades. But the authors went further by trying to cherry-pick the start and end dates. For instance, they stacked the cards against themselves by purposefully picking a very hot year to start the analysis and a cool year to terminate the study (1998 and 2012, respectively). Even this cherry-picked duration showed a warming trend. Furthermore, the warming trend was significant.

I asked lead author Dr. Karl for his comments on the significance of the paper and he told me,

Considering all the short-term factors identified by the scientific community that acted to slow the rate of global warming over the past two decades (volcanoes, ocean heat uptake, solar decreases, predominance of La Niñas, etc.) it is likely the temperature increase would have accelerated in comparison to the late 20^th Century increases. Once these factors play out, and they may have already, global temperatures could rise more rapidly than what we have seen so far.

So what does this all mean? Well we knew the globe was warming. The best evidence has always been by measuring the enormous amount of heat going into the oceans. But what this new paper shows is that the warming in the recent years has not stopped and has not even slowed down.

With 2015 so far running hotter than any year on record, and with May temperatures expected to be in the 0.79–0.84°C anomaly range, it becomes increasingly likely that we will set another all-time record this year. With hope, this will end the discussion of the so-called “pause” or “hiatus,” which never existed in the first place.