HOTHOUSE EARTH

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 HOTHOUSE EARTH

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• Risks of a Hothouse Earth : Even if carbon emissions are reduced to hold temperature rises at the 2°C guardrail of the Paris Agreement, changes already afoot in the environment such as melting permafrost and forest die-back could accelerate warming well into the future, potentially pushing our planet into what is being called a “Hothouse Earth” state.
• What is it? The Earth has been in hothouse (greenhouse) states before, and there are many types of it. They progress into ever-deeper states of heat and changes to the planet’s biosphere and climate. The end result is hellish, and for humans it would be a killer.
• Historical facts : 

1. The first state last occurred 125,000 years ago, during the previous interglacial phase of the Ice Ages. Atmospheric carbon dioxide levels were like those of pre-industrial times, at about 280 parts per million (ppm), and global temperatures were generally similar to today. Early humans were present, but in small numbers with only local impact on Earth’s ecology. During this interglacial phase, sea levels rose to some six metres above today’s as part of the Greenland and West Antarctic ice sheets melted, perhaps as changing ocean currents carried extra heat to the ice (how easily sea level can change). Then, animals (including humans) and plants simply adapted by migrating with the shoreline. Modern civilisation, with its sprawling coastal megacities, cannot do that at all.
2. We are set for the next stage. By burning fossil fuels we have launched atmospheric carbon dioxide levels beyond 400ppm – that’s an extra trillion tons of carbon dioxide. With this thicker thermal blanket, the Earth is absorbing more heat, with most of it going into the oceans. So, we have extreme weather events rising and ecosystems such as coral reefs already suffering drastic change. The last time the Earth saw these kinds of carbon dioxide levels was 3 million years ago, well before Homo sapiens appeared, in the “Mid Piacenzian Warm Period” of the Pliocene Epoch. The Earth still had a lot of polar ice, especially over Antarctica, but ice on Greenland and West Antarctica was much less extensive, and sea levels were some ten metres or more higher. 
3. A true Hothouse Earth emerged when carbon dioxide levels reached something like 800ppm – about double those of today. This was the world of the dinosaurs, 100m years ago. There was little or no ice on Earth and the polar regions had forests and dinosaurs which were adapted to living half the year in darkness. Dinosaurs flourished in a hothouse world of swamps and rainforest - but they had millions of years to evolve. The biosphere thrived, but equatorial regions tested the thermal limits of life. Much of the low-lying land had been claimed by the sea, which was now a worldwide warm bath in which animals steered a course to avoid the large, oxygen-depleted regions, a result of the sluggish ocean currents typical of an ice-free world. 

• The ultimate Hothouse Earth : It has not arrived, as it is a a runaway greenhouse world like that of planet Venus – heated to the point where the oceans are boiled away, with water vapour streaming through a punctured stratosphere, leaving a furnace-like surface. The lifeless surface of Venus shows the consequences of a runaway greenhouse effect.  Even burning all of our hydrocarbon fuels will not yet invite it.
• Hothouse Earth is a journey : It’s with many stops and even the next few steps. It’s the speed of the change that’s crucial. In a transition stretched out over millennia, humans could probably adapt to even a dinosaur-style hothouse. But if it’s going to come in centuries, or even in a human lifetime, there’ll be trouble.
• The panic and Zero Net Emissions: By 2021, various countries had started announcing their 2050 and 2060 targets of net zero emissions.

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