More Good News on Climate

Worse than we thought? Not lately. Consider some recent studies and data on hurricanes, rainfall trends, climate sensitivity, Atlantic Ocean circulation, and Antarctic temperature trends.

Major Hurricane Drought Continues

Not since Hurricane Wilma struck the Florida near Everglades City in October 2005 has a major (category 3 and larger) hurricane made landfall in the United States.

Hall and Hereid (2015), a study published last year in Geophysical Research Letters, reported that the nine-year “drought” in major U.S. hurricane landfalls from 2006 to the end of the 2014 hurricane season was “unprecedented” in the historical record, which extends back to 1851. The two scientists estimated that nine-year periods with no major U.S. hurricane strikes happen, on average, only once every 177 years.

There were also no major U.S. hurricane landfalls in 2015, extending the drought to a full ten years. “According to NASA, a stretch like this is only likely to happen once in 270 years,” CNN reports.

To be sure, our string of good luck is bound to run out eventually. The 2016 Atlantic hurricane season officially opens today, and NOAA says 1 to 4 major hurricanes are possible this year. Nonetheless, a 10-year hiatus in major U.S. hurricane landfalls with a probability of once every 270 years was not what Al Gore told us to expect in An Inconvenient Truth.

No Large Change in Rainfall during Past 150 Years

The most comprehensive study of global rainfall trends ever, based on 1000 weather stations in 114 countries, with each station having at least 100 years of observations, finds that “most trends over a century or longer are consistent with little precipitation change.”

Contrary to popular climate fears, over periods of a century or longer, dry areas are not becoming drier, wet areas are not becoming wetter, and deserts/jungles are not expanding or shrinking due to changes in precipitation patterns. The study, published in the Journal of Hydrology, concludes that “some caution is warranted about claiming that large changes in global precipitation have occurred during the last 150 years.”

How Insensitive!

Climate sensitivity is an estimate of how much global warming will occur after a doubling of carbon dioxide concentrations above pre-industrial levels. The higher the sensitivity estimate, the greater the projected warming from a given emissions scenario, and the more costly the potential impacts. The Intergovernmental Panel on Climate Change (IPCC) uses both observations and climate models to estimate sensitivity.

According to the IPCC’s 2007 Fourth Assessment Report (AR4), climate sensitivity is “likely to be in the range 2°C to 4.5°C with a best estimate of about 3°C.” According to the IPCC’s 2013 Fifth Assessment Report (AR5), climate sensitivity “is likely in the range 1.5°C to 4.5°C.” AR5 does not provide a best estimate due to a “lack of agreement” between modeling and observational studies. However, the average sensitivity of the models used in AR5 is 3.2°C.

In a study published last week by the American Geophysical Union, Irish meteorologist J. Ray Bates estimates climate sensitivity using both models and satellite measurements of outgoing infrared radiation from the tropics (i.e. how much heat the tropical atmosphere retains due to the greenhouse effect). He concludes that climate sensitivity is “≈1°C”—lower than the low end of the IPPC range in AR5. The study adds to the pile of recent papers indicating the climate system is less sensitive than the IPCC estimates.

Source: Michaels and Knappenberger* 

Sulfate Hypothesis Bites the Dust

To explain why global temperatures have been creeping rather than shooting up, many climate campaigners claim that sulfate aerosol pollution from fossil fuel combustion “masks” the warming effects of carbon dioxide emissions. Sulfate particles provide condensation nuclei for low-lying clouds, which cool the planet by blocking sunlight. Thus, the activists warn, when China and other developing countries finally install scrubbers and other pollution control devices, rapid warming will occur.

This sulfate hypothesis has always been dubious because it does not jibe with observed patterns of temperature change. If the hypothesis were correct, we would expect faster warming in the Southern Hemisphere, which combusts much less fossil fuel than the Northern Hemisphere. Instead, as climate scientists Patrick Michaels and Chip Knappenberger pointed out way back in 2005, “regions with the greatest temperature rise are eastern North America, Europe, and eastern Asia—the three leading industrialized areas of the world.”

Noting the “growing evidence” that one type of aerosol—black carbon or “soot”—is actually a strong warming agent, Michaels and Knappenberger concluded that the IPCC had overestimated the cooling influence of sulfate aerosol pollution and, thus, overestimated climate sensitivity as well.

Studies published last week in Nature further undermine the gloomy narrative that cleaning the air in China, India, and other industrializing nations will intensify global warming. The studies find that organic vapors from trees, especially when exposed to cosmic rays in clean air, produce an abundance of nuclei suitable for cloud formation.

The studies cast doubt on the assumption that the Earth will become less cloudy as developing countries curb their air pollution. For additional commentary, see “CLOUD shows preindustrial sky cloudier than we thought,” “CERN’s CLOUD experiment results suggest industrial revolution reduced cloud cover, cosmic rays have an impact too,” and “The cloud-climate conundrum.”

No Warming-Induced Ice Age on the Horizon

In An Inconvenient Truth, Al Gore warned that global warming could plunge Europe into an ice age by disrupting the Atlantic Meridional Overturning Circulation (MOC). Gore speculated that warming will melt the Greenland Ice Sheet, which will flood the North Atlantic with fresh water, which will make the sea surface too buoyant to sink, which will slow or shut down the overturning circulation that pulls warm tropical water up to the high northern latitudes.

As evidence, Gore cited a cooling event of 8,200 years ago, believed to have occurred when a giant Hudson Bay ice dam burst, allowing two Laurentide lakes to drain rapidly into the North Atlantic, disrupting the MOC. But anywhere from 100,000 to 200,000 cubic kilometers of lake water surged into the ocean.  In contrast, the rate of fresh water infusion from Greenland today is a comparative trickle—an estimated 220 cubic kilometers per year during 2008-2012.

Nonetheless, some scientists worry that a slowdown in the MOC during the past decade might be due to anthropogenic global warming. This week the UK Met Office reported the results of a new study “combining a state-of-the-art model of ocean dynamics with ocean observations from satellites, and ocean floats sampling below the surface.” The researchers note that their model “captured year-to-year variations and recent decadal trends with unprecedented accuracy.”

What did they find? In the words of lead researcher Laura Jackson: “The reanalysis reproduces the observed decrease in the Atlantic Meridional Overturning Circulation over the past decade, but finds that this was preceded by a period where the circulation intensified. This suggests that decadal timescale variability likely played a key role in the weakening of the circulation seen over the last decade.” The findings tally with the IPCC’s assessment that MOC collapse in the 21st century is “very unlikely.”

Antarctic Ocean Will Be Among the Last Places on Earth to Warm

Climate models typically project more warming at the poles than anywhere else on the planet. A study published this week in Nature Geoscience purports to explain why such polar amplification is not observed in the Southern Ocean surrounding Antarctica, in contrast to the rapid warming observed in the Arctic.

As summarized by Reuters, the Southern Ocean off Antarctica “may be among the last places on Earth to feel the impact of man-made climate change,” because gale force winds continually pull “ancient” cold water up from depths of 5,000 meters. “That upwelling helps explain why the surface of the Southern Ocean have [sic] warmed by just 0.02 degree Celsius (0.036 Fahrenheit) per decade since 1950, a fraction of the global average of 0.08 degree (0.144F), the study said.”

According to the study’s abstract, “These findings suggest the Southern Ocean responds to greenhouse gas forcing on the centennial, or longer, timescale over which the deep ocean waters that are upwelled to the surface are warmed themselves.”

On the significance of the study, I will defer to my go-to expert, Cato Institute climate scientist Chip Knappenberger:

This finding has potential implications for the future course of global sea level rise—perhaps the greatest concern of a warming planet. If surface warming rates remain low around Antarctica, their impact on ice loss there should be minimal.

On the other hand, warming was expected to lead to an increase of snowfall across Antarctica—partially offsetting ice melt from other locations around the world. The new findings may suggest that the snowfall increases may be slower to materialize than previously expected.

All in all, the new findings suggest that the Antarctic ocean will be among the slowest places on earth to warm—the implications of this still need to be explored, as they are undoubtedly complex. This is yet another example of the science most definitely NOT being settled.

* Figure explanation: Equilibrium climate sensitivity (ECS) estimates from new research beginning in 2011 (colored), compared with the assessed range given in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) and the collection of climate models used in the IPCC AR5. The “likely” (greater than a 66% likelihood of occurrence) range in the IPCC Assessment is indicated by the gray bar. The arrows indicate the 5 to 95 percent confidence bounds for each estimate along with the best estimate (median of each probability density function; or the mean of multiple estimates; colored vertical line). The right-hand side of the IPCC AR5 range is actually the 90% upper bound (the IPCC does not actually state the value for the upper 95% confidence bound of their estimate). Ring et al. (2012) present four estimates of the climate sensitivity and the red box encompasses those estimates. Likewise, Bates (2016) presents eight estimates and the green box encompasses them. Spencer and Braswell (2013) produce a single ECS value best-matched to ocean heat content observations and internal radiative forcing.