You Ought to Have a Look: Smoke, Clouds and Snowfall

You Ought to Have a Look is a feature from the Center for the Study of Science posted by Patrick J. Michaels and Paul C. (“Chip”) Knappenberger.  While this section will feature all of the areas of interest that we are emphasizing, the prominence of the climate issue is driving a tremendous amount of web traffic.  Here we post a few of the best in recent days, along with our color commentary.

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In this week’s YOTHAL edition, we’ll focus on some recent climate science findings that deserve further mention and are worthy of a deeper dive. If and when you have the time and/or inclination, you ought to have a look.

First up is a collection of papers that describe the results of a several experiments looking into cloud formation—or rather, into the availability and development of the aerosol particles that aid in cloud formation. The tiny aerosols are called cloud condensation nuclei (CCN) and without them, it is very difficult for clouds to form. 

It’s well known that sulfate particles, formed as a by-product of fossil fuel burning (primarily coal and oil), make for a good source of CCN. In fact, the change in cloud characteristics resulting from this form of air pollution are thought to have asserted a cooling pressure on the earth’s surface temperature—a cooling that has acted to offset a certain portion of the warming caused by the co-incidental emissions of carbon dioxide and other greenhouse gases.

Just how much warming has been offset by human-induced changes in cloud characteristics is one of the great unknowns in climate science today. Which is unfortunate, as it is a key to understanding how sensitive the earth’s climate is to increasing atmospheric concentrations of greenhouse gases. The less warming offset by enhanced cloud cooling, the less warming caused by greenhouse gas increases.

What the new research found was even in the absence of sulfate aerosols, there are plenty of other sources of potential CCN—a primary one being chemical emissions (known as volatile organic compounds, or VOCs) from plants. Through various processes, which the researchers found involve cosmic galactic rays, the plant VOCs can pretty efficiently transform and grow into CCN.

The bottom line from the new research findings is that the world was probably a cloudier place in the pre-industrial period than it has been generally realized. The implication is that human sulfate emissions haven’t altered cloud characteristics to the degree currently assumed—which means that current assumptions overestimate the magnitude of the anthropogenic cooling enhancement and thus overestimate the warming influence of greenhouse gas emissions (that is, the earth’s climate sensitivity is less than previously determined).

A good review of these three new experimental results (two of which were published in Nature and the other, simultaneously, in Science) and their implications is found in this news piece in Science that accompanied the papers’ publication. Here’s a teaser:

In other words, Earth is less sensitive to greenhouse gases than previously thought, and it may warm up less in response to future carbon emissions, says Urs Baltensperger of the Paul Scherrer Institute, who was an author on all three papers. He says that the current best estimates of future temperature rises are still feasible, but “the highest values become improbable.” The researchers are currently working toward more precise estimates of how the newly discovered process affects predictions of the Earth’s future climate.

At the very least, the Science overview article is worth a read. If you are interested further, you can have a look at the papers themselves (see links in reference list)—although, fair warming, they are quite technical.

Next up is an excellent review paper on wildfire occurrence in a warming world. The article, jointly authored by Stefan Doerr and Cristina Santín of Swansea University is part of a special issue of the Philosophical Transactions of the Royal Society B dedicated to “The interaction of fire and mankind.” Doerr and Santín take us through the extant literature of the trends and variability of fire occurrence and the factors influencing them. What they find is in stark opposition to the conclusion that you’d come to by reading the mainstream press. To hear the authors tell it:

Wildfire has been an important process affecting the Earth’s surface and atmosphere for over 350 million years and human societies have coexisted with fire since their emergence. Yet many consider wildfire as an accelerating problem, with widely held perceptions both in the media and scientific papers of increasing fire occurrence, severity and resulting losses. However, important exceptions aside, the quantitative evidence available does not support these perceived overall trends. Instead, global area burned appears to have overall declined over past decades, and there is increasing evidence that there is less fire in the global landscape today than centuries ago.

This is an eye-opening read in light of the hype surrounding the Ft. McMurray fires of recent weeks and the general warming-is-causing-more-fires-trope that is paraded out every time there is a fire burning somewhere in the US.  The authors go on to note that “[t]he media still promote perceptions of wildfire as the enemy even in very fire-prone regions, such as the western USA…”

And finally is a paper examining what the paleo-history of Greenland tells us about the relationship between higher temperatures and snowfall there. A research team led by University at Buffalo’s Elizabeth Thomas analyzed “aquatic leaf wax” records from sediment cores extracted from a lakebed in western Greenland to reconstruct a temperature and precipitation profile there over the past 8,000 years. Thomas and colleagues found that winter precipitation (snowfall) during a multi-millennial period of warmer-than-current temperatures in Greenland (extending from about 4,000 to 6,000 years ago) was substantially increased.

The proposed mechanism is that the warmer temperatures resulted in reduced sea ice in the nearby Baffin Bay and Labrador Sea which raised the regional moisture availability and increased snowfall.  The enhanced snowfall acted to offset some of the summer ice sheet melting that occurred with the higher temperatures, thereby slowing sea level rise. The authors suggest that a similar mechanism should accompany the current period of rising temperatures. They summarize:

The response of the western GrIS [Greenland Ice Sheet] to higher summer temperatures may have been muted due to increased accumulation in the middle Holocene. Our results suggest that in the future, as Arctic seas warm and sea ice retreats, increased winter precipitation may enhance accumulation on parts of the GrIS and partly offset summer ablation, particularly in areas close to modern winter sea ice fronts.

This result would seem to temper the scare stories of several meters of sea level rise in the coming century that have been circulating around the press—but, predictably, it’s been crickets from those press outlets.

Read more about in this press release, and/or from the paper itself.

 

References:

Bianchi, F., et al., 2016. New particle formation in the free troposphere: A question of chemistry and timing. Sciencedoi: 10.1126/science.aad5456.

Doerr, S. and C. Santín, 2016. Global trends in wildfire and its impacts: perceptions versus realities in a changing world.Philosophical Transactions of the Royal Society B, doi: 10.1098/rstb.2015.0345.

Kirkby, J., et al., 2016. Ion-induced nucleation of pure biogenic particles. Nature, 533, 521–526, doi:10.1038/nature17953.

Thomas, E., et al., 2016. A major increase in winter snowfall during the middle Holocene on western Greenland caused by reduced sea ice in Baffin Bay and the Labrador Sea. Geophysical Research Letters, doi: 10.1002/2016GL068513.

Tröstle, J., et al., 2016. The role of low-volatility organic compounds in initial particle growth in the atmosphere. Nature, 533, 527–531, doi:10.1038/nature18271.