Climate Change: A Very Short Introduction

by Mark Maslin

So although climate change has the potential to increase the range of many of these tropical diseases, the experience of Europe and the USA suggests that combating malaria is strongly linked to development and resources: development to ensure efficient monitoring of the disease and resources to secure a strong effort to eradicate the mosquitoes and their breeding grounds.

We know from the study of past records that the climate system can switch into a new state very quickly once a threshold has been passed. For example, ice-core records suggest that half the warming in Greenland at the end of the last ice age was achieved in only a few decades.

Irreversible melting of the Greenland and/or western Antarctic ice sheet, slowing down of the North Atlantic deep-ocean circulation, massive release of CH4 from melting gas hydrates, and the Amazon rainforest dieback will all be discussed.

The relationship between a climate forcing factor such as GHGs and the climate response is complicated. In an ideal world it would be a simple relationship with little or no delay, but we already know that there is inertia in the climate system, so that it responds to GHG forcing with a 10- to 20-year delay, depending on how much is being emitted.

Delayed and non-linear response (Figure 30c). In this case, the climate system may have an initial slow response to the GHG forcing but then respond in a non-linear way. This is a real possibility when it comes to climate change if we have underestimated the positive feedback in the system. This scenario can be equated to the car near the top of a hill: it takes some effort and thus time to push the car to the very top of the hill; this is the buffering effect. Once the car has reached the peak, it takes very little effort to push the car over it, and then it accelerates down the hill with or without help. Once it reaches the bottom, the car then continues for some time—the overshoot—and then it slows down of its own accord and settles into a new state.

Threshold response (Figure 30d). In this case, initially, there is very little response in that part of the climate system to the GHG forcing. However, on reaching a threshold, all the response takes place in a very short period of time, in a single, large step. In many cases, the response may be much greater than one would expect from the size of the forcing, and this can be referred to as a ‘response overshoot’. This scenario equates to the bus hanging off the cliff at the end of the original film The Italian Job: as long as there are only very small changes, nothing happens at all. However, a critical point (in this case weight) is reached and the bus (and the gold) plunges off the cliff into the ravine below. An example of this could be the Greenland ice sheet that has started to melt; the melting could suddenly accelerate, causing a catastrophic collapse.

There are also situations in which a threshold becomes a tipping point. You can think of a threshold as a point at which there is change in a system that can be reversed. But a tipping point is a threshold that, when crossed, means the system moves into a new state and this transition is irreversible.

The term ‘tipping points’ is used a lot in climate change research and discussions. However, care must be taken as there are two usages of this word. First, there are references to climate tipping points, which are the large-scale, irreversible shifts in the climate system, such as irreversible melting of ice sheets or the release of huge stores of CH4 from below the oceans. The other usage concerns societal tipping points, which occur when climate change has a major effect on a region or a particular country. For example, a 200 mile (~322 km) shift northward of the South-East Asian monsoonal rainfall belt is, in climatological terms, a small shift, not a fundamental climate tipping point. But for the countries where the rains no longer fall or those where it does for the first time, such a shift is a major climate tipping point, because their weather may have been permanently altered.

The IPCC projections for sea-level rise by 2100, if there are no significant curbs to carbon emissions, are between 0.50 m and 1.3 m.

Greenland and Antarctica together constitute one of the most worrying potential climate surprises. If the large ice sheets there melted completely, their contribution to global sea-level rise would be as follows: Greenland, about 7 m; the west Antarctic ice sheet, about 8.5 m; and the east Antarctic ice sheet, about 65 m.

The worst-case scenario, according to leading glaciologists, is that these ice sheets could add between 1 m and 1.5 m to the sea level by the end of the century, which would threaten many coastal populations around the world.

Our carbon emissions over the next few decades could determine the long-term future of the ice sheets and the livelihoods of billions of people who live close the coast.

As we have seen, there is already concern that global warming will cause significant melting of the polar ice caps. This will lead to more fresh water being added to the polar oceans. Climate change could, therefore, cause the collapse of the NADW, and a weakening of the warm Gulf Stream (Figure 31b). This would cause much colder European winters and more severe weather. However, the influence of the warm Gulf Stream is mainly seen in the winter and has only a small effect on summer temperatures. So, if the Gulf Stream fails, global warming would still cause European summers to heat up.

Monitoring has shown that the Gulf Stream has weakened by 15% since the middle of the last century. Evidence collated from this ocean monitoring and climate model predictions of the future in the very latest IPCC report suggest that collapse of the Gulf Stream is highly unlikely in the 21st century. The models do, however, show a significant weakening in the overturning

of the North Atlantic in this century, especially in the high-emission scenarios, and the problem is that we do not know where a potential tipping point leading to shut down of deep-ocean circulation might be.

These gas hydrate reservoirs could be unstable, as an increase in temperature or decrease in pressure would cause them to destabilize and to release the trapped CH4

If enough were released, it would raise global temperatures, which could lead to the release of even more gas hydrates—producing a runaway effect.

Scientists really have no idea how much CH4 is stored in the gas hydrates beneath our feet: estimates are of between 1,000 and 10,000 Gt (compared with ~800 GtC currently in the atmosphere), which is a huge range. Without a more precise estimate, it is very difficult to assess the risk posed by gas hydrates. 32.

The reason why scientists are so worried about this issue is because there is evidence that a super-greenhouse effect occurred 55 million years ago, during what is called the Palaeocene–Eocene Thermal Maximum (PETM). During this hot-house event, scientists think that up to 1,500 Gt of gas hydrates may have been released. This huge injection of CH4 into the atmosphere accelerated the natural greenhouse effect, producing an extra 5°C of warming.

The current consensus is that the ocean reserves of gas hydrate are likely to remain stable this century.

However, if carbon emissions are not curbed, then by the next century we could see this process speed up, leading to the release of some of the CH4 stored in the deep ocean.

It is clear that the gas hydrate below what was once permafrost is already melting, with bubbles observed in many Canadian and Siberian lakes. With the Arctic amplification temperature, rises will be nearly twice the global average in the northern polar regions, which will accelerate the gas hydrate melting. But we still do not have an indication of how much CH4 is stored beneath the world’s permafrost regions.

So at the moment, our best estimate suggests a global warming of 3°C could release between 35 and 940 GtC, which could add between 0.02°C to 0.5°C to global temperatures.

as it is a huge natural store of carbon. Originally it was thought that established rainforests such as the Amazon had reached maturity. Detailed surveys of all the rainforests of the world over the past four decades show this is incorrect. In the 1990s, intact tropical forests—those unaffected by logging or fires—removed roughly 46 billion tonnes of CO2 from the atmosphere. The sting in the tail is that this removal had diminished to an estimated 25 billion tonnes in the 2010s.

For the Amazon rainforest to survive, it requires not only a large amount of rain during the wet season but a relatively short dry season so as not to dry out.

The Amazon rainforest could not survive this longer dry season and would be replaced by savannah (dry grassland), which is found both to the east and south of the Amazon basin today.

Modelling the Amazon forest response to climate change is complicated because there are positive and negative feedbacks. For example, higher levels of atmospheric CO2 have a ‘fertilization’ effect on plants and trees, boosting photosynthesis and promoting growth.

Other climate models have not found such a profound dieback and the current IPCC review suggests a sustained dieback of the Amazon rainforest is unlikely this century—if the Amazon rainforest stays intact.

under the leadership of Brazilian President Jair Bolsonaro, deforestation rates have been on the rise accompanied by a significant increase in forest fires, many occurring in areas which do not usually suffer from them, indicating that many are being started deliberately.

In addition, scientists worry constantly about potential surprises in the global climate system that could exacerbate future climate change.

One way to ensure we avoid the worst effects of climate change and greatly reduce the likelihood of climate surprise is to keep climate change as small as possible.

Ceasing almost all flying and car journeys around the world had a small impact on our total GHG pollution.

The net zero emission target emerged from the important IPCC 1.5˚C global warming report published in 2018, which clearly showed that to achieve 1.5˚C there had to be zero carbon emissions by about 2050 and then negative carbon emissions for the rest of the century.

The UNFCCC approach has another problem, which is embedded in the concept of the nation-state and is a major issue in a global capitalist world with supposedly free trade.

For example, there could be a global agreement on how much carbon can be emitted per ton of steel or concrete produced. All countries could then agree only to buy steel or concrete produced in this low-emission way, which would make for a fairer trading scheme, with countries not losing out as a result of changes within their industries to lower GHG emissions.

The US Clean Air Act of 1990 required electrical utilities to lower their emissions of these pollutants by 8.5 million tonnes compared with 1980 levels. Initial estimates in 1989 suggested it would cost $7.4 billion; a report in 1998 based on actual compliance data suggested it had cost less than $1 billion.

The ETS covers half the EU’s CO2 emissions and 40% of its total GHG emissions.

The EU ETS has, however, been criticized because the emission caps have not been strict enough, leading to a very low-carbon price. In the UK, the addition of a ‘carbon price floor’, or a minimum government-set carbon price, has been essential in removing coal from the energy mix.

In addition, the new narrative of global ‘net zero carbon’ emissions by 2050 is very powerful—it changes the discussion from how much we can reduce emissions to when we will get rid of them altogether.

climate change may be more rapid and more pronounced than current estimates suggest, and unexpected and extreme events are likely to occur;

The major threat from climate change is its unpredictability

After the 2003 European heatwave, France completely reassessed its health response to the crisis. They changed everything, including: communication with the public; vulnerable individuals’ health checks; local health responses; and hospital admissions and treatment. It is estimated that in subsequent heatwaves the death toll was cut by over 75% because of these social adaptations.

There is some good news. GDP growth and carbon emissions have over the past decade become completely decoupled, with a large rise in world GDP compared with a much smaller rise in carbon emissions (see Figure 39

2020, the International Energy Agency (IEA) and International Monetary Fund (IMF) published a report recommending massive investment into clean energy, which would create millions of new jobs.

It was realized during the Covid-19 pandemic, that energy generation and use were the key to dropping carbon emissions.

Over the past decade there has been a massive increase in their efficiency, the best commercially available solar panels being about 23% efficient, which is significantly more than photosynthesis at about 1%.

in the short term, fuels derived from plants could be an intermediate low-carbon way of powering cars, ships, and aeroplanes.