Did you know that stopping the increase of carbon dioxide in the atmosphere is not enough to avoid global warming of two degrees Celsius? Emissions cannot be cut fast enough to keep the stock of greenhouse gases below this dangerous threshold level – unless a lot of the carbon that’s already in the air is taken out.

Greenhouse gas emissions

The Intergovernmental Panel on Climate Change (IPCC) publishes scenarios that describe how greenhouse gases emissions could evolve between 2000 and 2100. Over 100 of the 116 scenarios involve carbon capture schemes to remain below two degrees Celsius of global warming.

The median scenario assumes that a total of 810 billion tons (that’s around twenty years of global emissions at our current levels) are extracted from the atmosphere before 2100. So, what do these large-scale carbon removal technologies look like?

Carbon capture schemes

One carbon capture idea that’s not a winner involves increasing the capacity of our oceans to absorb more atmospheric carbon: ‘fertilising the oceans’ with tons of iron or other nutrients to stimulate plankton blooms that pull carbon out of the atmosphere. After thirteen major iron-fertilisation experiments in the open ocean, the UN Convention on Biological Diversity has put a moratorium in place, due to the toxicity of massive algal blooms and other unintended impacts.

Another loser is ‘solar radiation management’ that would have us inject sulphide gases into the atmosphere to block sunlight and cool down the atmosphere, rather than suck up any carbon emissions from the air. Ironically, we would pump even more substances into the environment. Some of the potential downsides include reductions in the protective ozone layer, in water precipitation and in our health from tons of returning sulphate particles.

The danger of these and all other geo-engineering technologies is that they are simply untestable on a small scale. Even if we could partition the atmosphere for test purposes, the evolving nature of the biosphere makes accurate predictions from such experiments impossible.

Other outlandish ideas such as sucking up diffuse carbon directly from the air using chemical filters are no better. Imagine if you can the energy usage and noise generated from just one of these gigantic extractor fans, planted near you. ‘Carbon capture and storage’ is a good concept for removing new emissions at source – from the top of a polluting chimney stack – but does not capture the billions of tons already in the atmosphere that also need to be removed.

The hard truth is that engineered carbon capture technologies do not exist on the large scale we need for scrubbing carbon from the air; and yet, our climate safety depends on this technology working and being in place.

Tree planting

A proven technology already exists that can work on the scale we have assumed; that can be deployed locally almost anywhere; that costs very little and builds itself. It is called a tree.

Rooted in place, trees and local canopy cover create microclimates that differ from other tree-less areas. They modify the effects of solar radiation, air temperature, humidity and precipitation; providing shade and wind protection and contributing to cooling the surrounding air by the evaporative process of transpiration. They can literally change the climate around us.

The opportunity before us is to copy what’s working. The innovation needed is not an engineered alternative to trees and plants – it’s to be more inventive in how we embed trees and plants into our built environment and how we change our land use practices. How can we plant more trees, help more of them survive, find new and attractive uses for timber?

The winner this year and every year are trees. Urban trees, agroforestry,  silviculture, tiny forests, rewilding, afforestation, pocket parks, vertical forests, back garden trees. More trees in more places; trees and people co-existing in ways that will benefit all of us. Given the scale of the carbon drawdown, the best time to plant a tree was twenty years ago. The second best is now.

For more big ideas, visit the local action about planting more trees.