The UN report found that greenhouse gases are likely to push global temperatures at least 1.5 ° C above pre-industrial conditions over the next 20 years, fueling heat waves , more frequent and severe floods and droughts. Once that happens, removing carbon is essentially the only way to bring the climate back to a safer area, as the greenhouse gas lasts for hundreds to thousands of years in the atmosphere. (A final alternative may be some form of geoengineering that sends heat back into space, but this controversial idea has all kinds of concerns.)
The model used to create the report’s most optimistic scenario, which limits warming to 1.5 ° C, assumes the world will find ways to remove about 5 billion tonnes of carbon dioxide per year by the middle. century and 17 billion by 2100. (The scenario is known as SSP1-1.9, and these numbers are based on an analysis of previous data by Zeke Hausfather, climatologist at the Breakthrough Institute and contributing author for the assessment of UN.)
This requires the rise of technologies and techniques capable of removing as much CO2 from the atmosphere each year as the US economy emitted in 2020. In other words, the world would need to put together a whole new carbon-sucking sector running on emissions. scales of all cars, power plants, airplanes and factories in the United States, over the next 30 years.
We could eliminate less than that, but only if we reduce emissions even faster, do we resign ourselves to greater climate risks – or both.
In the above model, almost all of the carbon removal is achieved through an “artificial” approach known as bioenergy with carbon capture and storage, or BECCS. Basically, this requires growing crops that consume CO2, and then using the harvested biomass to produce heat, electricity, or fuels, while also capturing and storing the resulting emissions. But despite the billions and billions of tons of carbon removal that climate models rely on through BECCS, this has only been done in small-scale projects to date.
The smallest amount of removal remaining in the model is done by “natural” solutions such as reforestation and tree planting (see illustration below).
We know that forests, soils, peatlands and other natural systems take up significant levels of carbon dioxide, but it has proven difficult to develop markets and systems that incentivize, measure and verify it in a way. reliable. Meanwhile, other technical approaches are also immature, including carbon sucking machines and various ways to speed up the processes by which minerals and oceans absorb and store CO2.
The IPCC assessment identified many other limitations and challenges.
On the one hand, while removing carbon reduces the level of greenhouse gases in the atmosphere, the report notes that this effect can be offset to some extent. Modeling studies have shown that oceans and land begin to release more CO2 in response to this changing atmospheric chemistry over certain time periods, compromising the benefits.
Additionally, while removing carbon could gradually mitigate temperature increases and ocean acidification, it does not magically reverse all climate impacts. Notably, it would take centuries to bring the oceans back to the levels around which we built our coastal cities, the report said. There could be almost irreversible damage to ice caps, coral reefs, rainforests and some species as well, depending on global warming before we dramatically reduce emissions and increase carbon removal.