The race to limit global warming

At the heart of climate science lies the greenhouse effect — how the Earth’s atmosphere traps some of the heat that reaches us from the sun.

This warming is essential for our survival. Without it, the average global temperature, if all solar radiation was reflected back into space, would be around 18C rather than the 14C that we actually enjoy.

Climate change can occur when humans add more heat-absorbing gas to the atmosphere than is natural. This can lead to disruptions in life on the planet.

Water vapour is a more important contributor to the natural greenhouse effect than other gases, but carbon dioxide is the main human-made contributor. This is due to the large amounts of CO2 produced by fossil fuels like coal, oil, and natural gas. Trillions of tonnes of these carbon-rich compounds exist in geological strata across the world — the remains of countless plants, animals and microbes.

Over a time period of decades, we have increased atmospheric CO2 by more that 40% since preindustrial times.

The next most important warming agent is methane (CH4). It’s produced by energy, industrial, and agricultural production. Each molecule of methane can absorb far more heat than CO2 but, fortunately, there is much less of it in the atmosphere and it does not hang around for quite so long — on average about 12 years.

Other greenhouse gases include fluorine compounds and nitrous oxide.

Of course, the climate has varied throughout Earth’s history as a result of the complex interaction between processes including volcanic activity, solar variability, and cyclical changes in ocean currents.

Some climate skeptics have attempted to attribute the warming of around 1C since industrial activity began to natural variability and not human activities. This view is scientifically untenable because of the rapid rise in temperature and the lack of plausible natural explanations.

Already, the 1.1C temperature change is causing disruption in weather patterns. Rainfall distribution is changing. Warmer temperatures hold more moisture and energy. This means that storms and flooding are becoming more common. Droughts and intense heat in other regions are causing crop failures and forest fires.

The momentum of industrial activity and the delayed response of the atmosphere and oceans mean a further increase to at least 1.5C warming is inevitable — and many scientists expect 2C to be breached even if the world takes the strongest action that we can realistically expect.

There is still uncertainty about the future extent and regional variations of climate change. Temperatures are rising faster than the tropics in the Arctic and the polar regions. One pressing question is how much climate change will be exacerbated by positive feedbacks, whereby one warming effect drives another — such as how melting permafrost in the Siberian tundra releases methane and carbon dioxide.

Rising sea levels are one of the more predictable consequences of global warming. The average rise across the world’s oceans over the past 30 years has been about 10cm, propelled both by melting ice from Greenland and Antarctic and by the thermal expansion of water.

This century is expected to see higher sea levels. A report from the US National Ocean Service in February Prognosticated a riseThe increase in the American coastline will be between 25cm and 30cm over the next thirty years, with devastating floods occurring 10x more often. By 2100, the increase is likely to be at least 60cm — and could be more than a metre.

Fighting global warming depends, above all, on drastically cutting the world’s carbon emissions. The most carbon dioxide per unit of energy produced by coal is followed closely by oil and natural gas.

The world is now investing in alternative sources of non-carbon energy, especially solar and wind, as well as batteries and other technology to store this power for when the weather is clear and calm. The electricity generated from renewable sources could be used to generate fuel for transport. It does this by breaking down water into its components: hydrogen and oxygen. Another source of carbon-free energy is nuclear power.

Many companies have committed to “net zero” targets, resolving to reduce their carbon emissions and offset the impact of those they cannot cut, by investing in schemes to remove CO2 from the atmosphere.

Reforestation is the most efficient way to achieve this. Because trees absorb CO2 from the air as they grow, it reduces the available land for farming.

The more tech-intensive methods include removing the CO2 from the atmosphere, or from the power station emissions, and storing it underground.

But these “negative emissions” technologies cannot be scaled up in the short term. The long-term success of these technologies will depend on individuals, businesses, and governments making a genuine political and economic commitment in order to decarbonise their activities.