New research out of Purdue University finds that a global warming event called the PETM made parts of the tropics too hot for living organisms to survive. And though the PETM happened many millions of years ago, these new scientific revelations are pertinent to the present day. The reason is that human activity in the form of fossil fuel burning is now rapidly causing the globe to heat up. And such warming, if it continues, could well turn large sections of the tropics into a dead zone.

PETM — Warm-up Sparks Global Upheaval, Extinction

The PETM was a big global warm up that happened 56 million years ago as the Paleocene epoch passed into the Eocene. It is numbered as one of many hothouse extinctions occurring in the geological record. And it is generally thought to have been one of the milder such events — especially when compared to the biosphere wrecking ball that was the Permian.

(NASA tool shows that business as usual greenhouse gas emissions would force average maximum July temperatures over large sections of the world to warm to 40-45 C [104-113 F] by the 2090s. For many regions, such a high degree of heat is incompatible with crops and human habitability. In the deep past, hothouse events were found, in recent research, to render large sections of the tropics uninhabitable to most forms of life. Image source: NASA.)

During the PETM, global temperatures jumped by 5 degrees Celsius above an already warm base-line over the course of about 6,000 years. And research indicates that the resulting heat stress set off massive wildfires, forced land animal species to move pole-ward, and killed off a big chunk of the ocean’s bottom dwelling foraminifera.

Parts of the Tropical Biosphere Seem to Have Died

However, past scientific consensus held that the tropics still managed to support life during the PETM due to a kind of thermostat-like heat regulation preventing the equatorial region from becoming too warm. Temperatures were thought to have remained within a range that would have continued to support life in this lower latitude zone. So it was only thought that the tropics experienced die-offs during ancient and more intense warming events like the Permain of 250 million years ago.

The new research by Purdue scientists calls that theory into question. Their findings show that temperatures crossed a key threshold — becoming too hot to support life throughout sections of the tropics and rendering large areas uninhabitable.

Matthew Huber, professor in the Earth, Atmospheric, and Planetary Sciences Department at Purdue University and study co-author notes:

“The records produced in this study indicate that when the tropics warmed that last little bit, a threshold was passed and parts of the tropical biosphere seems to have died. This is the first time that we’ve found really good information, in a very detailed way, where we saw major changes in the tropics directly associated with warming past a key threshold in the past 60 million years.”

Half of Human Population Lives and Farms in the Tropics

During the present day, about half the human population, a good chunk of the world’s life forms, and a considerable amount of global farming occupies the tropics. However, according to recent research by the Max Planck Institute, parts of the tropical zone could be rendered basically uninhabitable to human beings by mid Century as the Earth heats up due to fossil fuel burning. And already, the critical region of Equatorial Africa and the adjacent Middle East are experiencing record droughts, water stress, and instances of hunger, famine and related food insecurity as global temperatures rise to 1 C or more above 1880s averages.

(Climate zone habitability is a function of what forms of life can exist in a given region at a given range of temperatures. Warming in the tropics is expected to impact human habitability by mid Century. Warming, however, is also expected to impact crop yields well into the middle latitudes. U.S. food production is therefore likely to be negatively impacted by rising global temperatures. Video source: Peter Carter.)

The serious concern is that as the world warms up — a humanitarian crisis of unprecedented scope could emerge as whole countries become unable to support their populations. As entire regions become too hot to live in. And as major swaths of global farmland become non-productive.

The present narrative hints that human civilization can somehow adapt by shifting farm zones northward. However, it’s worth noting that boreal regions do not support the same highly productive soils as the tropical and temperate zones that are now under threat due to rising temperatures. In addition, the nations of the world have thus far shown considerable reluctance to accepting refugee populations from destabilized zones. And as the world heats up, desperation will only increase as waves of refugees seek to remove themselves from what could well become a kind of global warming produced dead zone.

The Perdue research underscores a very real risk that we are now facing. It shows that the tropics did not self regulate temperature in a range conducive for life during the PETM. And these findings reinforce present temperature and soil moisture research trends placing human habitability and crop production under threat due to fossil fuel based warming this Century.

(UDATED)

Links:

Global Warming Can Breach Limits for Life

Climate Impacts of the PETM

NASA

Peter Carter

Hat tip to Suzzanne

Hat tip to Colorado Bob

Hat tip to Andy in San Diego