More aerosols, means more clouds, which means cooler temperatures. Now that we are cleaning up aerosols worldwide, this may explain why the Earth is getting slightly warmer – more sunlight reaches the surface
A paper published today in Science claims the transition from “pristine” to “slightly polluted” atmosphere at the beginning of the industrial revolution in the 18th century had a “dramatic aerosol effect [of increasing] clouds” over the oceans. According to the authors,
“transition from pristine to slightly polluted atmosphere yields estimated negative forcing of ~15 watts per square meter (cooling), suggesting that a substantial part of this anthropogenic forcing over the oceans occurred at the beginning of the industrial era, when the marine atmosphere experienced such transformation.”
By way of comparison, the IPCC alleged change in radiative forcing from CO2 [plus alleged positive water vapor feedback] since the beginning of the industrial era is +1.8 watts per square meter*, or 8.3 times less. According to an accompanying editorial to the paper, the authors “show that even small additions of aerosol particles to clouds in the cleanest regions of Earth’s atmosphere will have a large effect on those clouds and their contribution to climate forcing.”
*Per the IPCC formula: 5.35*ln(395/280) = 1.8 W/m2 at the top of the atmosphere [or only about 1.8* (1/3.7) = 0.5 W/m2 at the surface]
h/t to The Hockey Schtick
Smith et al. in 2004 finds that sulfur based aerosols, the kind that also get emitted from volcanoes, have been increasing since 1850, but have recently leveled off since about 1975…about the time that the US Clean Air Act really started kicking in (from updates in 1970) and other industrialized countries followed suit.
1850-2000: Methods and Results” -PNNL
Their paper:
Click to access PNNL-14537.pdf
From “Just Add Aerosols“: Science 6 June 2014: Vol. 344 no. 6188 p. 1089 DOI: 10.1126/science.1255398
The more carbon dioxide and other greenhouse gases in the atmosphere, the stronger the climate warming that results. Likewise, the more aerosol particles suspended in the atmosphere, the greater the ability of these particles either to scatter sunlight back to space and cool the planet or to absorb sunlight in the atmosphere, thereby warming the atmosphere while cooling Earth’s surface. However, not all such climate forcing processes depend linearly on the concentrations of their forcing agent. The climatic effects of aerosols are complicated by their interactions with clouds (1). On page 1143 of this issue, Koren et al. (2) show that even small additions of aerosol particles to clouds in the cleanest regions of Earth’s atmosphere will have a large effect on those clouds and their contribution to climate forcing.
The paper:
From aerosol-limited to invigoration of warm convective clouds
Abstract:
Among all cloud-aerosol interactions, the invigoration effect is the most elusive. Most of the studies that do suggest this effect link it to deep convective clouds with a warm base and cold top. Here, we provide evidence from observations and numerical modeling of a dramatic aerosol effect on warm clouds. We propose that convective-cloud invigoration by aerosols can be viewed as an extension of the concept of aerosol-limited clouds, where cloud development is limited by the availability of cloud-condensation nuclei. A transition from pristine to slightly polluted atmosphere yields estimated negative forcing of ~15 watts per square meter (cooling), suggesting that a substantial part of this anthropogenic forcing over the oceans occurred at the beginning of the industrial era, when the marine atmosphere experienced such transformation.
Editors summary: Invigorating convection in warm clouds
Atmospheric aerosols—tiny airborne particles—affect the way clouds form and how they affect climate. Koren et al. investigated how the formation of warm clouds, such as those that form over the oceans, depends on pollution levels (see the Perspective by Remer). Aerosols affect cloud formation in cleaner air disproportionately more than in more polluted air. Before the widespread air pollution of the industrial era, it seems, warm convective clouds may have covered much less of the oceans than they do today.
eVince says:
June 6, 2014 at 9:32 pm
You ask,
“Could trees be attempting to regulate the thermal environment? To keep temperatures cool enough for good growth and health?”
I think you may be correct !
I remember working in a poly tunnel / greenhouse full of evergreen Escallonia shrubs. The smell of VOCs they produce always got stronger when the heat went up! Higher metabolic rate, more aromatics. If these products form aerosol by combining with gasses in the environment they are producing sites/liquid aerosols onto which water vapour can condense. I think this is an evolved mechanism to reduce water loss through evapotranspiration by ensuring it , lost vapour, can quickly condense near to the plant. Apply to a forest of trees with heat added and a rainforest forms.
Plant aromatics are produced to attract pollinators or repel predators too. Why not attract water also!
How many trees does it take to make a cloud?
http://www.interactions.org/cms/?pid=1033860
” Around half of all cloud seeds are thought to originate from nucleated particles, but the process of nucleation is poorly understood.
Sulphuric acid is thought to play a key role, but previous CLOUD experiments have shown that, on its own, sulphuric acid has a much smaller effect than had been assumed. Sulphuric acid in the atmosphere originates from sulphur dioxide, for which fossil fuels are the predominant source. The new result shows that oxidised biogenic vapours derived from alpha-pinene emitted by trees rapidly form new particles with sulphuric acid. Ions produced in the atmosphere by galactic cosmic rays are found to enhance the formation rate of these particles significantly, but only when the concentrations of sulphuric acid and oxidised organic vapours are relatively low. The CLOUD paper includes global modelling studies which show how this new process can account for the observed seasonal variations in atmospheric aerosol particles, which result from higher global tree emissions in the northern hemisphere summer.
It shows that sulphuric acid aerosols do indeed have a significant influence on the formation of clouds, but they need the help of trees.”
Does the rate of deforestation follow the temperature rise? Northern hemisphere and all that! More land area. Or do the remaining trees pump out more VOCs as the temp goes up! To cool things down!
Oceans are pretty good at producing their own sulphur containing aerosol precursor gasses, Dimethylsulfoniopropionate. Relatively low amounts, in less polluted environment open to GCR ionisation . So it is not just trees doing it. The stuff in the oceans do it,too. Contribute to the nucleation of aerosols that is.
When ‘sulphur based aerosols’ form they need an organic partner or to combine with an electrically attractive partner, either way sulphuric acid droplets need a mate to form particles stable enough to form aerosols it would seem!
I despair. Three papers published in Science in 2005 (Wielicki et al, Wild et al and Pinker et al) all showed that natural aerosol and cloud changes caused the drop in temperature globally from 1945-1975 – when clouds and aerosols caused ‘global dimming’ – NOT anthropogenic sources which can be shown to be localised (10-20% of the global surface, mostly in the northern hemisphere), whereas the dimming occurred also in ‘pristine’ oceanic areas (I reviewed this work in my book ‘Chill’, because ALL the IPCC models had assumptions based on the false premise of anthropogenic sulphur as causal factor. The ‘brightening’ began in 1980 – both in natural aerosols and reduced cloud cover, especially optically dense low-cloud – roughly 4% fall from 1980 to 2001. This brightening also occurred in rural China! despite the proximity to SO2 megacities.
Sulphur emissions are largely at 50-100m height and fall-out within a few hundred to several thousand kilometres depending on the weather conditions. The only sulphur emissions powerful enough to depress global temperature are volcanic and need to penetrate the stratosphere to stay aloft long enough to cool the globe.
The Big Bear Solar Observatory ‘earthshine’ data independently support the cloud cover changes.
WHY are these facts hardly EVER referenced????? Because they completely destroy the credibility of the IPCC ‘hindcasting’ models.