The Tyranny Of Climate Change
The current interglacial warm period, the Holocene, started ∼11,500 years ago. At its start, among the dramatic changes in climate was a notable increase in rainfall, triggered by summer insolation values higher than those of today. This caused what is called the African Humid Period in North Africa—a time when the Sahara was dotted with large and small lakes, savannah grasslands, and in some regions, humid tropical forests and shrubs. The African Humid Period ended abruptly ∼5000 ybp (years before present) in many locations, such as western North Africa and northern Kenya. In other places, such as the central Sahara and the southern Arabian Peninsula, change occurred more gradually, taking several millennia. Regardless of the pace of change, those areas are tracts of arid desert today, and the animals and humans who had previously thrived in those formerly verdant regions have either moved or had to adapt to much harsher conditions. This is but one example of nature at its most capricious—the tyranny of climate change.
Scientists still argue over the timing of the African Humid Period (AHP), which corresponds roughly to the Holocene Climate Optimum, a time much warmer than today. Most people do not realize that the Sahara desert and Horn of Africa were once lush green lands filled with animals and humans. Looking at these areas today gives little hint of their more congenial past. One point of contention among climate scientists is the speed with which the transition occurred. In a new paper, “Abrupt Shifts in Horn of Africa Hydroclimate Since the Last Glacial Maximum,” published in Science, Jessica E. Tierney and Peter B. deMenocal present evidence that, in some areas, this change was fairly rapid. Here is the abstract of their paper:
The timing and abruptness of the initiation and termination of the Early Holocene African Humid Period are subjects of ongoing debate, with direct consequences for our understanding of abrupt climate change, paleoenvironments, and early human cultural development. Here, we provide proxy evidence from the Horn of Africa region that documents abrupt transitions into and out of the African Humid Period in northeast Africa. Similar and generally synchronous abrupt transitions at other East African sites suggest that rapid shifts in hydroclimate are a regionally coherent feature. Our analysis suggests that the termination of the African Humid Period in the Horn of Africa occurred within centuries, underscoring the nonlinearity of the region’s hydroclimate.
As the authors state, the fundamental cause of the AHP—dramatic increases in summer precipitation triggered by orbital forcing of African monsoonal climate and amplified by oceanic and terrestrial feedbacks—is widely accepted by scientists. However, the abruptness with which the AHP began and, most particularly, ended is still debated. In an accompanying perspective article, “Out of the African Humid Period,” Edouard Bard, of the Collège de France and CEREGE, explains why scientists are so interested in this natural example of climate change.
The increasingly arid conditions at the end of the African Humid Period forced human agropastoral societies to improve their organization in order to optimize natural resources, in particular freshwater supplies. As a result of growing demographic pressure in an environment that was again becoming hostile, Neolithic communities were forced to concentrate in river valleys and to develop irrigation systems. These complex transformations help explain the rise of the Egyptian, Sumerian, and Harappan civilizations that flourished along major rivers such as the Nile, Euphrates, Tigris, and Indus.
Certainly, if these changes were triggered by a reduction in insolation—the amount of energy received from the Sun—the effects would have been felt world wide. From proxy records, scientists believe that summer insolation in the subtropical zone has slowly decreased as a result of changes in Earth's orbit around the Sun. But the question of timing remained: slow and gradual or abrupt and dramatic.
To try and resolve the question of timing the Tierney and deMenocal constructed a new record of precipitation in the Horn of Africa. They measured the deuterium-to-hydrogen ratio (D/H) of leaf waxes taken from marine sediment cores. This isotope ratio is directly linked to the isotopic composition of precipitation, which is linked to total rainfall. The location of their test site and the region involved are shown in the map below.
By comparing their Gulf of Aden record with published records, Tierney and deMenocal conclude that the African Humid Period ended abruptly within a few centuries and was synchronous in the western and eastern part of Africa. By considering modern climate observations and model simulations, they propose that East African rainfall responded in a nonlinear way to surface temperatures in the Indian Ocean—in other words a tipping point was reached.
As nature takes from some regions it gives to others. In another recent article, this one in PNAS, it seems that deposits of windblown dust originating from the Sahara may have been responsible for the prehistoric condition of the Florida Everglades. An analysis of sediments deposited over the past 4600 years provides a record of the vegetation and soil nutrient patterns and shifts in hydrology, revealing some of the processes that have previously remained obscure. In “Holocene dynamics of the Florida Everglades with respect to climate, dustfall, and tropical storms.,” P. H. Glaser and a team of researchers from the University of Minnesota's Department of Earth Sciences shed some new light on changes in Florida's famous swampland.
Glaser et al. show that dust deposition mediated by frequent tropical storms was an important source of nutrients for the Everglades. Indeed, what was North Africa's loss was Florida's gain. The transition to desert from a more humid climate in the Sahara, led to the transport of dust to North America, with a salubrious effect on the Everglades. This period may have been the cause of the striking surface patterning seen in the Everglades.
Then, about 2800 years ago, a climate shift in the tropical Atlantic and Gulf of Mexico led to new weather patterns and a drier climate in the Florida peninsula. The climatic change was probably induced by a shift in the Bermuda High to the southeast, shunting tropical storms to the south of Florida into the Gulf of Mexico. It also sharply decreased the level of arriving Saharan dust, leading to a gradual loss of soil nutrients. Nature gives and nature takes away.
Ancient humans left a record of life on the green Sahara.
Here are but two examples of dramatic and rapid climate change in the recent past; change observed by our ancestors and even recorded by them as petroglyphs and cave paintings. There are a number of important points that can be drawn from these examples:
- Rapid changes in climate can happen anywhere at any time.
- Change in one area may elicit change in others far away—all environments are connected.
- The proximate cause of the desertification of the Sahara was change in insolation caused by Earth's ever changing orbit.
- These climate changes were definitely not caused by human CO2 emissions.
If you had been living in the Sahara region 5,000 years ago and things started getting drier, wildlife began to disappear and what was a benign environment started to turn into a desert wasteland you would have had one of two courses of action: adapt or move. This has always been the case until modern times—Angkor Wat, the Mayan Yucatán, the ancient civilizations of the Indus and Yellow rivers were all beset by climate change. The difference between then and now is that ancient humans tended not to blame their civilizations for the changing climate.
Is there any doubt, that if the Sahara was green today and it suddenly took a turn for the more arid, North Africa turning into a desert would be blamed on anthropogenic global warming? Or that a sudden shift in rainfall and vegetation type in Florida would be sized on by climate alarmists as proof that humanity was befouling the planet? Just as the ignorant attempt to use severe weather events to bolster calls for the deindustrialization human civilization, any such dramatic and widespread regional changes would be chalked up to human actions.
It is not that humans don't affect Earth's climate, we do. But so does every other living thing on Earth. Microscopic diatoms in the ocean poisoned Earth's atmosphere with oxygen, causing mass extinctions and a transformation of the biosphere that took 1.6 billion years. Flowering plants and then grasses radically change the landscape and Earth's albedo. Animals too interact and modify their surroundings. Elephants, buffalo and other large animals actively change their environments to favor conditions they prefer. Vast schools of krill fill the oceans and hidden swarms of termites decompose fallen plants, releasing those dreaded greenhouse gasses, without which the Earth would be a frozen ball.
Like everything else alive on this planet, people change the environment around them and are, in turn, changed by that environment. Life is an ever changing saga where the cast of creatures constantly evolves as new species arise and others vanish into extinction. Yet somehow those who claim to defend nature—even worship it as a deity—think every last species is sacrosanct and must be defended to the last penny in the public coffers. Don't these green paragons understand that nature is not static? That all is change in nature, and species that cannot change die out? The truth is nature is a tyrant, cruel and uncaring.
The Sahara was once a lush paradise, with a little bit of global warming it might be again.
Alas, the predispositions of academics, the idle rich and undereducated youth all center on blaming humanity for any natural calamity, any unwelcome change, any perceived threat to the most obscure and useless creature. In the rush to blame humanity for every evil that befalls the world, our sense of perspective has been lost. Sure the Earth has been warming, but not by much, and no one knows how much human activity contributes to that warming or even if the warming is bad. If things were warmer the Sahara might once again be a garden spot. But then, when any change is bad, those who agitate against humanity constantly find new outrages to rail against. It takes a special kind of stupidity to get nature all wrong and then blame humanity when your ignorance is revealed.
Be safe, enjoy the interglacial and stay skeptical.