Recently researchers have noticed several areas where large amounts of methane are bubbling to the surface of the Arctic Ocean. The press has quoted one of the observers as saying that this is “terrifying.” Another recent report has declared that the Arctic tundra is now a net source of carbon emissions. Perhaps.
Has the Arctic passed a tipping point? Circumstantial evidence is pretty scary, but it needs to be put in the context of overall emissions from the Arctic biome. We need comprehensive inventories of these lands and waters to understand the extent to which these one-off events are truly cause for alarm. There is little doubt that the tundra is rapidly transforming, and there have been a distressing number of discoveries of such large gas eruptions in Siberia.
Make note of the Paleocene-Eocene Thermal Maximum (PETM). This was a spike of 5-8˚C in the atmospheric temperature about 55.5 mya. Officially the academic community does not know what caused the PETM, but increasing evidence from stable isotopes is compelling that it was caused by pulses of CO2 and massive releases of methane. Methane has an intrinsically high forcing ability and a relatively short lifespan in the atmosphere. It is interesting that the PETM lasted only about 200,000 years, whereas other forcing events that involved large amounts of carbon dioxide and methane persisted for much longer.
There is a lot published on the ecosystem disruptions in the oceans and on land that occurred during the PETM and it is a model for what is unfolding as we warm our atmosphere during this century. The impacts of the PETM did not result in one of the five mass extinctions, but many species went extinct and there was wholesale disruption of the Earth’s ecosystems.
Recently a commentary in Science by two leading experts notes that the Amazon forest is very close to a tipping point. Deforestation and burning of the forest is now synergistic will increasing frequency of extreme drought. As a source of humidity, i.e. the trees, is reduced, the hydrology of the entire Amazon Basin is shifting toward drier conditions. The outcome of this is the creation of savanna, which has far less carbon uptake potential than the rainforest. The region that we have always assumed would absorb CO2 from the air is now mostly impaired. Along the way to this new state it will release enormous amounts of carbon and is becoming a massive positive feedback to the climate system.
We live in interesting times. What continues to amaze me is that as a species we can quantify and understand in explicit detail how we are destroying the Earth’s ability to support the civilization that has made this awareness possible. It is surreal.
Even stranger is the magic of CO2. Carbon dioxide is necessary for life and over billions of years the Earth has developed a dynamic flux of carbon among atmosphere, rocks, and living systems. This is part of the rhythms of our planet in which changes occurring over millennial timescales provides the substrate for the evolution of species and ecosystems.
Without anthropogenic influences during the modern era, CO2 should exist in our atmosphere well below 300 ppm. We are at 411 ppm as I write this. The last time our atmosphere contained ~400 ppm was the Pliocene, about 3 mya, and sea level was at least 6 meters higher than it is now. It is a rare gas that nourishes us all, yet if there is too much of it even if relatively rare, it can disrupt the climate that made possible the development of civilization. During this decade we have repeatedly been surprised by the sometimes extreme responses of the Earth System to about 1˚C warming.
CO2 and the other non-condensing greenhouse gases are responsible for the radiant energy structure of the atmosphere that makes the overall temperature of the Earth consistent with life. If CO2 were to be zeroed out, that structure would collapse and the Earth would become icebound with an average temperature below -20˚C. It is true that water vapor, a condensing greenhouse gas, is responsible for about 70% of the greenhouse effect, but only if CO2 provides the radiant energy structure of the atmosphere to allow sufficient capture of heat in the layer of air where we live.
The bottomline is that CO2 is the master thermostat for our planet and it has a rather narrow range of setpoints that are consistent with our needs. All of civilization and agriculture developed during the last 8,000 years, the stable period known as the Holocene, aka The Goldilocks Climate, because it was neither too cold nor too hot. It is entirely possible that the development of civilization is simply a one-off that may be just a blip in the unfolding evolution of the Earth System.
Amazingly, we understand these things about our planet even as we wreck it.
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