Earth warming
KEV McKay recently states that, “the long-term trend for the earth is a cooling one”. This is not entirely true. It would be more correct to say that the earth’s temperature fluctuates through time in response to various forcing mechanisms and feedbacks.
Sure, the earth was in a molten state during formation some 4.5 billion Years ago (Gya), but then 2.4 Gya the earth was engulfed in the massive Huronian glaciation which was driven by the Kenorland supercontinent break-up and blooms of biogeochemical oxygenic photosynthesis. Two “snowball earth” events occurred 635 million years ago (Mya) and 715 (Mya), the Maranoan and the Sturtian glaciations. Both episodes were characterised by total covering of ocean and land surfaces with ice and were likely a response to intense magmatic events that accompanied the dislocation of the Rodinia supercontinent. Fresh basaltic provinces enhanced the weather ability of continental surfaces which “sucked” huge quantities of CO2 out of the atmosphere. The earth was plunged into the coldest periods of its existence. The average temperature of planet earth is 14.9 degrees C. 56 Mya Earth experienced a rapid global warming event that saw average global temperatures rise 5-8 degrees C in just 20,000 years- a geological blink. We refer to this as the paleoceneeocene thermal maximum or P.E.T.M. During this time the earth’s average temperature was about 7 degrees C warmer than today ie 22 degrees C. The likely cause was a massive excursion of 13C depleted carbon from sub-marine methane clathrates and thermogenic methane and
CO2 from hydrothermal vent complexes.
Marine ecosystems suffered the worst. Almost 50% of deep sea benthic forams went extinct with ocean acidification and ocean hypoxia implicated as the main drivers. In some iomes, 20% of land plants went extinct
You say that, “man-made climate change is hyperbole”. Our current rate of acidification exceeds the PETM and human missions are now an order of magnitude (10 times greater) than the carbon emissions during the PETM.
Our models suggest the earth will reach two degrees C above pre-industrial by 2037. The last time the earth was two degrees C above pre-industrial was 130 000 years ago in the Eemian (the last interglacial period) and sea levels were 6-9 metres higher than today. Without reductions in our greenhouse gas emissions, our climates by 2150 could compare to the warm and mostly ice-free Eocene, an epoch that characterised the globe 50 Mya.
I cannot stress enough that it is the unprecedented rate of global change caused by humans that is the problem. We are on track to warm the earth somewhere between three to six degrees C by 2100, something nature would take 10,000 years to do. The potential for climate hysteresis if we cross too many tipping points could well become an existential crisis for humanity.
GEOFF CASTLE, USQ researcher