Sometimes one just scratches the head and wonders!
In yesterday’s post, I wrote, “strongly resonated with a recent item on Peter Sinclair’s excellent blog Climate Denial Crock of the Week …”
Here is that item, republished with Peter’s kind permission:
Global Warming Continues to Accelerate
March 25, 2013
A new study of ocean warming has just been published in Geophysical Research Letters by Balmaseda, Trenberth, and Källén (2013). There are several important conclusions which can be drawn from this paper.
- Completely contrary to the popular contrarian myth, global warming has accelerated, with more overall global warming in the past 15 years than the prior 15 years. This is because about 90% of overall global warming goes into heating the oceans, and the oceans have been warming dramatically.
- As suspected, much of the ‘missing heat’ Kevin Trenberth previously talked about has been found in the deep oceans. Consistent with the results of Nuccitelli et al. (2012), this study finds that 30% of the ocean warming over the past decade has occurred in the deeper oceans below 700 meters, which they note is unprecedented over at least the past half century.
- Some recent studies have concluded based on the slowed global surface warming over the past decade that the sensitivity of the climate to the increased greenhouse effect is somewhat lower than the IPCC best estimate. Those studies are fundamentally flawed because they do not account for the warming of the deep oceans.
- The slowed surface air warming over the past decade has lulled many people into a false and unwarranted sense of security.
The main results of the study are illustrated in its Figure 1.
In this paper, the authors used ocean heat content data from the European Centre for Medium-Range Weather Forecasts’ Ocean Reanalysis System 4 (ORAS4). A ‘reanalysis’ is a climate or weather model simulation of the past that incorporates data from historical observations. In the case of ORAS4, this includes ocean temperature measurements from bathythermographs and the Argo buoys, and other types of data like sea level andsurface temperatures. The ORAS4 data span from 1958 to the present, and have a high 1°x1° horizontal resolution, as well as 42 vertical layers. As the authors describe the data set,
“ORAS4 has been produced by combining, every 10 days, the output of an ocean model forced by atmospheric reanalysis fluxes and quality controlled ocean observations.”
Accelerated Global Warming
As illustrated in Figure 1 above, the study divides ocean warming into three layers for comparison – the uppermost 300 meters (grey), 700 meters (blue), and the full ocean depth (violet). After each of the Mt. Agung, Chichón, and Pinatubo volcanic eruptions (which cause short-term cooling by blocking sunlight), a distinct ocean cooling event is observed in the data. Additionally, after the very strong El Niño event of 1998, a cooling of the upper 300 and 700 meters of oceans is visible as a result of heat being transfered from the surface ocean to the atmosphere.
One of the clearest features in Figure 1 is the rapid warming of the oceans over the past decade. As we have previously discussed, the warming of the shallower oceans has slowed since around 2003, which certain climate contrarians have cherrypicked to try and argue that global warming has slowed. However, more heat accumulated in the deeper oceans below 700 meters during this period. The authors describe the ocean warming since 1999 as,
“the most sustained warming trend in this record of OHC. Indeed, recent warming rates of the waters below 700m appear to be unprecedented.”
Their results in this respect are very similar the main conclusion of Nuccitelli et al. (2012), in which we noted that recently, warming of the oceans below 700 meters accounts for about 30% of overall ocean and global warming. Likewise, this new study concludes,
“In the last decade, about 30% of the warming has occurred below 700 m, contributing significantly to an acceleration of the warming trend.”
Some ‘Missing Heat’ Found
Kevin Trenberth past comments about ‘missing heat’ drew considerable attention. The phrase refers to the fact that the heat accumulation on Earth since about 2004 (e.g. from warming oceans, air, and land, and melting ice) that instruments were able to measure could not account for the amount of global heat accumulation we expected to see, based on the energy imbalance caused by the increased greenhouse effect, as measured by satellites at the top of the Earth’s atmosphere.
These new estimates of deeper ocean heat content go a long way towards resolving that ‘missing heat’ mystery. There is still some discrepancy remaining, which could be due to errors in the satellite measurements, the ocean heat content measurements, or both. But the discrepancy is now significantly smaller, and will be addressed in further detail in a follow-up paper by these scientists.
So what’s causing this transfer of heat to the deeper ocean layers? The authors suggest that it is a result of changes in winds related to the negative phase of the Pacific Decadal Oscillation and more frequent La Niña events.
Good News for Climate Sensitivity? Probably Not
Recently there have been some studies and comments by a few climate scientists that based on the slowed global surface warming over the past decade, estimates of the Earth’s overall equilibrium climate sensitivity may be a bit too high. However, as we previously discussed, these studies and comments tend to neglect the warming of the deep oceans below 700 meters.
Does the warming of the deep ocean support these arguments for lower equilibrium climate sensitivity? Probably not, as Trenberth explained (via personal communication),
“it contributes to the overall warming of the deep ocean that has to occur for the system to equilibrate. It speeds that process up. It means less short term warming at the surface but at the expense of a greater earlier long-term warming, and faster sea level rise.”
So the slowed warming at the surface is only temporary, and consistent with the ‘hiatus decades’ described by Meehl et al. (2011). The global warming end result will be the same, but the pattern of surface warming over time may be different than we expect.
The real problem is that in the meantime, we have allowed the temporarily slowed surface warming to lull us into a false sense of security, with many people wrongly believing global warming has paused when in reality it has accelerated.
Global Warming Wake Up Call
Perhaps the most important result of this paper is the confirmation that while many people wrongly believe global warming has stalled over the past 10–15 years, in reality that period is “the most sustained warming trend” in the past half century. Global warming has not paused, it has accelerated.
The paper is also a significant step in resolving the ‘missing heat’ issue, and is a good illustration why arguments for somewhat lower climate sensitivity are fundamentally flawed if they fail to account for the warming of the oceans below 700 meters.
Most importantly, everybody (climate scientists and contrarians included) must learn to stop equating surface and shallow ocean warming with global warming. In fact, as Roger Pielke Sr. has pointed out, “ocean heat content change [is] the most appropriate metric to diagnose global warming.” While he has focused on the shallow oceans, actually we need to measure global warming by accounting for all changes in global heat content, including the deeper oceans. Otherwise we can easily fool ourselves into underestimating the danger of the climate problem we face.
“Global warming has not paused, it has accelerated.”
Now I should end it there. But I can’t!
American readers worried about the drought? Do watch this short video from Paul Douglas. (Apologies for the ad. at the start.)
For worldwide readers who have seen the massive changes in ‘normal’ weather this winter, take a look at this, first published on the NASA Earth Observatory website:
While a high-pressure weather system brought warmer than normal temperatures to Greenland and northern Canada in March 2013, much of North America, Europe, and Asia shivered through weeks of unseasonably cool temperatures. The contrasting temperatures are no coincidence: the same unusual pressure pattern in the upper atmosphere caused both events.
Atmospheric pressure patterns are constantly in flux, as air masses of differing temperatures and densities move around the skies. One key measure of pressure that meteorologists track closely is known as the Arctic Oscillation (AO) index, the difference in relative pressure between the Arctic and the mid-latitudes. Changes in the AO have can major impacts on weather patterns around the world.
When the AO index is in its “positive” phase, air pressure over the Arctic is low, pressure over the mid-latitudes is high, and prevailing winds confine extremely cold air to the Arctic. But when the AO is in its ”negative“ phase, the pressure gradient weakens. The pressure over the Arctic is not as low and pressure at mid-latitudes is not as high. In this negative phase, the AO enables Arctic air to flow to the south and warm air to move north.
In late March, the AO dropped as low as -5.6. (See this chart published by the Washington Post’s Capital Weather Gang to see how this compares with other periods when AO values reached record-low levels).
The temperature anomaly map above, based on data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite, shows how this affected temperatures in the Northern Hemisphere. The map displays land surface temperature anomalies between March 14–20, 2013, compared to the same dates from 2005 to 2012. Areas with above-average temperatures appear in red and orange, and areas with below-average temperatures appear in shades of blue. Much of Europe, Russia, and the eastern United States saw unusually cool temperatures, while Greenland and Nunavut Territory were surprisingly warm for the time of year.
Many parts of the Northern Hemisphere saw near record-breaking cool temperatures as the value of the AO fell. The United Kingdom experienced its 4th coldest March since 1962. In late-March, two-thirds of weather stations in the Czech Republic broke records. Germany saw its coldest March since 1883. And Moscow had its coldest March since the 1950s.
- Climate Central (2013, March 19) From Heat Wave to Snowstorms, March Goes to Extremes. Accessed April 1, 2013.
- Der Spiegel Online International (2013, March 28) White Easter: Germany Faces Coldest March Since 1883. Accessed April 2, 2013.
- Earthsky (2013, March 22). Officially spring, but feels like winter for many in U.S. Accessed April 1, 2013.
- Met Office (2013, March 28) Coldest March for the UK since 1962. Accessed April 2, 2013.
- NOAA Arctic Oscillation (AO). Accessed April 1, 2013.
- Prague Daily Monitor (2013, March 28) Cold weather breaking records. Accessed April 2, 2013.
- Washington Post (2013, March 24) Record blocking patterns fueling extreme weather: detailed look at why it’s so cold.Accessed April 1, 2013.
NASA Earth Observatory image by Jesse Allen and Robert Simmon, using MODIS data from the Land Processes Distributed Active Archive Center (LPDAAC). Arctic Oscillation data from the NOAA National Weather Service Climate Prediction Center. Caption by Adam Voiland.
Sorry, I know I went on a bit!