African Dust The New CO2?

Chad, located along the southern edge of the Sahara Desert, is the dustiest place on Earth. Recognizing that aerosols plays a vital role in climate and biophysical feedback in Earth's environmental system, climate researchers are turning to dust as a major driver of climate change. A new article, to be published in PNAS, identifies the Bodélé Depression in Chad as the producer of about half the mineral aerosols emitted from the Sahara. According to Richard Washington et al. dust could be a “tipping element” where “small features of the atmospheric circulation, such as the Bodélé Low-Level Jet, could profoundly alter the behavior of this feature.” With the impact of CO2 diminished due to a cooling climate climate, researchers are searching for new hazards: Is African dust the new carbon dioxide?

The role of aerosols, both mineral and biological, has been under intense scrutiny in recent years. The IPCC AR4 reported aerosols as one of the most potent climate forcings about which science understood very little. The paper “Dust as a tipping element: The Bodélé Depression, Chad” is but the latest paper to call attention to the importance of African dust. I have previously reported on the impact of Saharan dust storms on the tropical Atlantic (see “African Dust Heats Up Atlantic Tropics”) and how aerosol levels from dust storms and volcanoes alone would account for much of observed global temperature rise (see “Arctic Aerosols Indicate Melting Ice Not Caused By CO2”). Now, in the PNAS paper, researchers claim that the Bodélé area may be a “tipping element” in the context of climate change, due to its location and prodigious dust output.

The Bodélé Depression is Chad’s lowest point and it is one of the world’s most active sources of dust storms. On November 9, 2006, NASA’s Terra satellite took this picture of a dust storm in the Bodélé Depression showing two visible plumes. The dust plumes appear as pale beige brush strokes against a tan background. To the southwest of the dust storm is Lake Chad, which appears mostly dark green. Irrigation and declines in rainfall have reduced the size of the lake, once as big as Lake Erie in North America, to only 5 percent of its size in 1966.


Dust storm captured by the Moderate Resolution Imaging Spectroradiometer (MODIS). NASA.

So much dust is produced by the Bodélé Depression that it provides most of the mineral dust to the Amazon forest. In a paper in Environmental Research Letters, Ilan Koren et al. reported that, based on satellite observations, dust is continuously transport 3,000 miles (5000 km) from Saharan sources to the Caribbean Sea and North America in the Northern summer and to the Amazon basin during the Northern winter. According to the PNAS paper:

About 40 million tons of dust are transported annually from the Sahara to the Amazon basin. Saharan dust has been proposed to be the main mineral source that fertilizes the Amazon basin, generating a dependence of the health and productivity of the rain forest on dust supply from the Sahara. Here we show that about half of the annual dust supply to the Amazon basin is emitted from a single source: the Bodélé depression located northeast of Lake Chad, approximately 0.5% of the size of the Amazon or 0.2% of the Sahara. Placed in a narrow path between two mountain chains that direct and accelerate the surface winds over the depression, the Bodélé emits dust on 40% of the winter days, averaging more than 0.7 million tons of dust per day.

There is evidence that during the Last Glacial Maximum atmospheric dust concentration was as much as an order of magnitude greater than present-day values, but dust levels are highly variable. Modern observations suggest that between 1960 and 2000 annual mean African dust generation may have varied by a factor of 4. It is thought that minor modifications to global circulation patterns could cause dust production from the Bodélé to increase significantly or reduce it to near zero. “We argue that the Bodélé is indeed capable of profound changes in future emissions,” state Washington et al. “Although the full consequences of these change have not yet been quantified, the case exists for doing so.”


TOMS satellite annual average aerosol index (AI) 1979 –1992. Washington et al.

Indeed, recent analysis of aerosols' complex heating and cooling influences have led to a greatly reduced impact for atmospheric CO2 levels. As previously reported, a large aerosol cooling implies a correspondingly large climate sensitivity. Conversely, reduced aerosol cooling implies lower GHG warming, which in turn implies lower model sensitivity. The upshot of this is that CO2 sensitivity values used in models for the past quarter of a century have been set too high. With global temperatures flattening and even declining since 2002 it looks like all those climate models that had been tweaked to match last century's temperature curve—thereby pumping up the importance of human carbon dioxide emissions—have quietly left the world stage.

The new found emphasis on dust has been bearing scientific fruit in a rash of recent papers including one published in Quaternary Research in November of 2007. This paper by Elsa Jullien et al. reports a link between low-latitude “dusty events” and “icy Heinrich events,” which occur at higher latitudes. As you may recall from previous posts, Heinrich events happened when the American ice sheets became unstable. That gave rise to enormous ice surges which formed vast flotillas of drifting ice floes in the Atlantic Ocean and noticeable increases in ice rafted debris deposits. The last event (H1) some 14,000 years ago set the stage for the onset of the Holocene warming. According to the abstract of the paper by Jullien et al.:

We explore low-latitude Heinrich events equivalents at high resolution, in a piston core recovered from the tropical north-western African margin. They are characterized by an increase of total dust, lacustrine diatoms and fibrous lacustrine clay minerals. Thus, low-latitude events clearly reflect severe aridity events that occurred over Africa at the Saharan latitudes, probably induced by southward shifts of the Inter Tropical Convergence Zone. At a first approximation, it seems that there is more likely synchronicity between the high-latitude Heinrich Events (HEs) and low-latitude events (LLE), rather than asynchronous behaviours.

Heinrich events, numbered 1 through 6, occurred during a period of extensive sea-ice in the North Atlantic similar to today’s Arctic Sea. Heinrich events are relatively brief and tend to occur at the boundaries of major climatic transitions as indicated by δ18O proxy measurements. Event number six, the oldest accepted event, occurred around 60,000 years ago. Heinrich event 1 marked the onset of the termination which signaled the end of the last interglacial. It is thought that fresh water released during the Heinrich events disrupted deep-water formation, thereby prompting switches between glacial and interglacial modes of thermohaline circulation. If these recent papers linking dust to HEs prove accurate then it is possible that large amounts of dust from the Sahara is a sign of cooling, not global warming.


Dirty icebergs are characteristic of Heinrich events. NOAA.

Again science has uncovered significant factors not considered by the IPCC's models, with significant impact on the doomsday predictions made by climate change alarmists. The important link between dust and climate was only suspected when the IPCC was busy cranking out dire global warming scenarios with their computer models. None of the models accurately accounted for aerosols and their affect on other forcings like albedo and the hydrological cycle. Now some scientists even suspect that dust is an important trigger for larger climate change events, a “tipping element.”

“Several factors distinguish the Bodélé as a potential tipping element,” argue Washington et al. “it is the largest single source of mineral dust on the planet, producing about half of the Sahara’s mineral aerosol loadings.” They list the following reasons for thinking dust could be a tipping element: “Mineral dust plays a key role in modifying climate through interaction with cloud physics and radiative heating. It is also involved in numerous biophysical feedbacks both in the oceans and on land.” Even so, the Bodélé is a very small region and the effects of dust on the world's environmental system are still mostly unknown. The authors almost sadly conclude “The Bodele, at this stage, qualifies as a potential tipping element until more work can be done to quantify the radiative impacts and biogeochemical consequences of mineral aerosols.”

Is dust then the new carbon dioxide, a villain to base predictions of disruptive climate change on? Probably not, aerosols' complex environmental interactions can't be dumbed down into a simple formulation as rising CO2 levels were. When trying to frighten the public simple sells, and dust's interaction with the environment is far from simple. But one simple point is becoming clearer and clearer: Climate modeling centered on CO2 levels, instead of providing a solid foundation for global warming theory, has proven to be less substantial than the dust blowing out of Africa.

Be safe, enjoy the interglacial and stay skeptical.


Dust storms in Africa can affect climate world wide.

The reported loss of Africa

The reported loss of Africa dust and its warming influence on the Atlantic Ocean has a far more dire and immediate consequence. The same series of satellite data used by these climate modelers has shown a more than 26% decline in net primary productivity of the Atlantic, read forced extinction of green plants, the phytoplankton. This massive loss of ocean plankton has staggering effects up and down the food chain destabilizing the Atlantic ecosystem.

One of its most damaging forcing effects is in the role in destruction of Atlantic fish stocks. While it is fashionable and politically correct to point fingers for fisheries declines only at the bad fishers the loss of ocean pasture capacity is worse. Further those fish were not mere farm animals awaiting slaughter they are or were the worms of the surface ocean whose toil of life churned and recycled ocean nutrients greatly enriching those ocean pastures. As we starve and remove the worms, fish and other marine life, of the seas we destroy the ecosystem.

The same data series that shows the decline in African dust and ties it as the primary cause of Atlantic Ocean warming also shows that dust decline is due to greening of the grassy regions of N. Africa which are made greener by the massive dose of CO2 we've emitted over the past century. That dose of CO2, a deadly airborne carbon bomb, will remain for centuries even if were to never emit another molecule of CO2, which of course isn't going to stop. So as high CO2 nurtures green plants on land making better ground cover and reducing dust the CO2 also acidifies the ocean and worst missing dust denies the ocean vital mineral micronutrients. The more than one thousand billion tonnes of fossil CO2 already in the air is more than sufficient to seal the doom of ocean plants and ecosystems. The ONLY hope is to replenish and restore those ocean plants and the ocean pastures.

Only ocean plants can compete with the acid forming reaction H2O+CO2+H2CO3 carbonic acid. And it matters NOT if we reduce todays or tomorrows CO2 emissions as the deadliest problem is yesterdays CO2. We simply must immediately begin to replenish the micronutrients to the oceans and restore ocean plant life. By restoring ocean plant life to the level seen some 26 years ago when the satellite data started coming in we might expect to see those restored ocean plants taking the same amount, 4-5 billion tonnes of CO2 and converting it to ocean life instead of its destiny today acid death.

During those same 26 years scientists from around the world in both public and private sectors have spent hundreds of millions of dollars researching the prospect and promise of ocean restoration by means of replenishing the vital mineral micronutrients our fossil fuel age has denied the oceans. The means and ability to safely replenish and restore the oceans is at hand and will cost a tiny fraction of the cost of the hundreds of billions being spent on climate change. It can and must begin immediately as reports clearly show the CO2 tipping point for some oceans is as near as 2030, a mere 20 years from today. This is not a deadline by which we must begin to replenish and restore the oceans to deal with the deadly effects of yesterdays CO2; it is the deadline by which we must succeed at the job.

Every moment of debate and argument, and these debates and arguments have gone on non stop for more than 20 years, forces CO2 acidification and nutrient deprivation to drive once verdant ocean pastures into lifeless seas, or rather seas of toxic slime.

Replenish and restore the oceans to the condition of health they and we enjoyed 26 years ago.

Add Soot to the IPCC Fallback Position

See the article by Marc Morano on ClimateDepot: "Skeptical UN IPCC Scientist Mocks: 'CO2 control is failing so the 'soot' fall-back position is being adopted by those who like to pretend people effect global climate"

There have been some papers...

...Linking Saharan Dust to Atlantic Ocean temperature changes-and also linking it to hurricanes. I would bet that Saharan Dust is linked to the AMO-which impacts atmospheric circulation, precipitation in such places as Florida and the Sahel and of course Hurricanes...but I'm not even sure how all the connections work out. Here's some references:

Foltz, G. R., and M. J. McPhaden, 2008. Trends in Saharan dust and tropical Atlantic climate during 1980-2006. Geophysical Research Letters, 35, L20706, doi:10.1029/2008GL035042.

The Role of Aerosols in the Evolution of Tropical North Atlantic Ocean Temperature Anomalies
Amato T. Evan, Daniel J. Vimont, Andrew K. Heidinger, James P. Kossin, Ralf Bennartz, Science 8 May 2009: Vol. 324. no. 5928, pp. 778 - 781, DOI: 10.1126/science.1167404

Thanks for the references

Thank you for providing the references. The second paper was the basis for my earlier column, "African Dust Heats Up Atlantic Tropics," but the first one I was unaware of.

Global emissions

Global emissions will stop growing only if all major countries agree; what is the chance of that happening? What is the point of reducing our emissions if others increase theirs even more? Globally, this is evident in increasing average air and ocean temperatures, widespread melting of snow and ice and rising average sea level. In Canada, we are already seeing rising temperatures, shifting rainfall patterns, and increases in certain types of hazardous weather, such as heat waves. Global sea level rose by about 120 meters during the several millennia that followed the end of the last ice age (approximately 21,000 years ago), and stabilized between 3,000 and 2,000 years ago. Sea level indicators suggest that global sea levels did not change significantly from then until the late 19th century. Bob from Abu Reels.