A crash course in climate change: 24 key facts everyone needs to know

Flooded fields at Lake Ellesmere in Canterbury

Here are a few key facts David Nelles and Christian Serrer, the authors of Small Gases, Big Effect, want you to know about climate change.

1. The rise in global temperature

In the northern hemisphere, the average ground-level air temperature stayed relatively constant in the thousand years leading up to the Industrial Revolution. Since the end of the 19th century, however, we have observed a rise in the global temperature. From the time temperature records first began in 1880, up to 2016, the average global ground-level air temperature increased by more than 1°C.

2. Understanding the “natural greenhouse effect”

Most of the sun’s rays penetrate the Earth’s atmosphere and reach its surface. These rays are absorbed by the Earth and are then released as thermal radiation, or heat. Without the presence of certain gases in the atmosphere, such as water vapour, carbon dioxide, ozone, nitrous oxide and methane, this thermal radiation would simply escape back into space.

This would make the climate around 33°C colder, and the entire planet would freeze over. Instead, thanks to this layer of naturally occurring gases, thermal radiation is absorbed and then released again, in all directions – including back down towards the surface of the Earth. This process of warming is known as the “natural greenhouse effect”. The Earth’s atmosphere consists mainly of nitrogen and oxygen. The concentration of natural greenhouse gases is actually vanishingly small. Carbon dioxide, ozone, nitrous oxide and methane together make up only about 0.04 percent of the Earth’s atmosphere. Water vapour makes up on average around 0.25 percent.

3. The rise of man-made greenhouse gases

Since the start of industrialisation, there has been a sharp increase not only in the average global air temperature but in the concentration of carbon dioxide and other greenhouse gases in the atmosphere. Human activity, in particular the burning of fossil fuels, is the reason for this change. Gases released by human activity are called anthropogenic or “man-made” gases, because, just like natural greenhouse gases, they prevent the escape of thermal radiation from the Earth back into space. As a result the Earth’s surface absorbs more thermal radiation than it otherwise would.

Trees blowing in the wind with yellow smog sky

4. Man’s impact on the carbon cycle

In 2015, China was by far the biggest emitter of Oceans, soils and vegetation all release carbon dioxide into the atmosphere. They also absorb it. In the past 10 years, humans have released 39 gigatonnes (39 billion tonnes) of CO2 each year. About 28 percent of it is captured by vegetation and soils, and about 22 percent is absorbed by the oceans, but most of the rest – 44 percent – remains in the atmosphere. In a relatively short time period, human activity has released so much more CO2 into the atmosphere that it has knocked the natural carbon cycle off kilter. Much of this carbon was underground for millions of years in the form of coal, natural gas or crude oil. One consequence of this large and sudden release of CO2 is that the oceans have become more acidic; another is that CO2 concentrations in the Earth’s atmosphere are higher than they have ever been in the past 800,000 years.

5. What are the sources of carbon dioxide emissions?

The burning of fossil fuels (coal, petroleum and natural gas) to generate energy accounted for approximately 85 percent of global CO2 emissions in 2014. Cement production was responsible for 5 percent, and changes in land use for 10 percent. Another source of CO2 emissions is the large-scale felling of trees in Europe and North America several hundred years ago. Today, it is mainly tropical rainforest that is being cut down and cleared to build roads, develop pasture land, produce timber or to plant crops for export such as oil palms, bananas, soy and coffee. From 2000 to 2009 forested areas have been lost at an average rate of 35 football fields per minute.

In 2015, China was by far the biggest emitter of carbon dioxide from the burning of fossil fuels, ahead of the US and the European Union. However, a different picture emerges if we look at historical emissions, which still contribute to global warming today because of the long atmospheric lifetime of CO2. Between 1918 and 2012, the EU and US emitted much more CO2 than China.

Emissions resulting from the manufacture of goods are allocated to the country where they are produced. If per capita emissions were calculated by allocating emissions to the country in which the goods are consumed, we would see a reduction in the per capita emissions of China, India and Russia, and a rise in the emissions of European countries and the US.

6. What are the sources of methane emissions?

In the period from 2000 to 2009, 29 percent of global man-made methane emissions came from fossil fuel extraction. Nearly as much methane is generated by livestock farming. Almost another quarter is released by decomposing waste in landfill sites. Similar decomposition processes are triggered when rice fields are flooded. The remaining emissions come from burning biomass (for example wild fires) and manufacturing biofuel.

7. What are the sources of nitrous oxide emissions?

Agriculture is by far the largest contributor to nitrous oxide emissions, with a share of 59 percent. The fertilisers used in farming contain nitrogen compounds that are partly broken down by bacteria in the soil. This causes nitrous oxide to be released into the atmosphere. Livestock also produce nitrous oxide through their excretions. Rivers also release nitrous oxide, since nitrogen compounds are washed into waterways (through sewage and fertilisers used in farming). The remaining emissions come from other sources, such as human excrement.

Sun shining through a hurricane
Flooding at Canterbury’s Lake Ellesmere – 18 percent of the world’s heavy rainfall events on land can be attributed to global warming.

8. The arctic’s sea ice is melting

The consequences of climate change are particularly clear in the Arctic, because the air temperature there is increasing significantly faster than the average air temperature of the Earth as a whole. From 1979 to 2016, the minimum area covered by sea ice in the Arctic fell by approximately 43 percent. In the same period, the thickness of the ice cover also shrank, meaning that the total volume fell by around 77 percent.Snow and ice reflect a huge proportion of incoming solar radiation back into space. If an area covered with snow or ice melts, the darker area beneath – for example, water or rock – will then become exposed, reflect much less radiation and absorb heat and warm up further. This causes further warming of the Earth, resulting in even more snow and ice melt, and even more warming again. Since an increasing surface area of sea ice now melts during each Arctic summer, the ocean absorbs a much greater amount of heat. Since the ocean is correspondingly warmer, the ice now melts not only because of solar radiation, but also, increasingly, because of the warmer seawater which surrounds it.

The impact of climate change

9. Glaciers are retreating

Almost all glaciers observed worldwide are gradually losing mass. Not only are the glaciers retreating, there is also less snow coverage in the northern hemisphere. Since 1966, the surface area of land covered with snow has decreased at an average rate of 213 square kilometres per year.

10. Greenland’s ice sheet is melting

More than 99 percent of the global land ice mass is in the ice sheets of Greenland and Antarctica. The Greenland ice sheet is the second largest on Earth and covers almost the entire land area of Greenland, and in many places it is more than 3km thick. The melting of this ice sheet is one of the reasons for rising sea levels, and between 2002 and 2016 was responsible for a sea level rise of approximately 0.8mm per year. Greenland’s ice sheet has been losing mass at an accelerating rate in recent years.

11. Antarctica’s ice sheet is declining

Antarctica is covered by the largest sheet of ice on Earth. Most of the ice in Antarctica is on land, and the rest lies as connected, floating coastal ice shelves. There is so much ice in Antarctica that the sea level would rise by about 58m if the entire ice sheet were to melt. Unlike in the Arctic, the area covered by sea ice in the Antarctic region showed an annual average increase of 0.16 percent between 1979 and 2016. However the ice sheet is declining in terms of overall mass. To a large extent, this loss is due to the melting of the West Antarctic ice shelf by the relatively warmer seawater beneath. Overall, from 2003 to 2016, there was an annual mass loss of roughly 141 gigatonnes (141 billion tonnes).

12. Oceans are warming and becoming more acidic

Oceans cover more than 70 percent of the Earth’s surface. They are of enormous importance for maintaining our climate, as they transport vast quantities of heat around the world. They also act as a buffer against global warming, because they absorb some man-made CO2 emissions as well as a large part of the energy that is retained on Earth as a result of the man-made greenhouse effect. From 1971 to 2010, the oceans absorbed 93 percent of the energy that had been kept within the Earth’s atmosphere. As a result, the average surface temperature of the oceans has risen – by 0.8°C in the period from 1880 to 2015 – and the deeper layers beneath have also warmed.The oceans are becoming more acidic as they absorb about 22 percent of man-made CO2 emissions. In this way the oceans are attenuating global warming, but at the expense of their sea life, which is being increasingly affected by the warming and acidification of its habitat.As gases are less soluble in warm liquids than in cold ones, the oceans are becoming less able to absorb man-made CO2 emissions. Consequently, they are becoming a less effective buffer to global warming. The oxygen level in the oceans is also decreasing, placing an additional strain on sea life.

13. Changes in oceanic circulation

The Atlantic Meridional Overturning Circulation (AMOC) is a part of what is known as the “global conveyor belt”. Together with the Gulf Stream and the North Atlantic Current, it transports large quantities of heat from the tropics to the North Atlantic, thereby helping to maintain the moderate climate in northwest Europe.The warm, salt-rich surface water flowing north releases its heat into the atmosphere in the North Atlantic. This leaves the seawater cooler and denser, causing it to sink and then flow back southwards in the deep ocean. In the south, different water masses combine in the deep ocean, which, helped by surface winds, brings the deeper water back to the surface. The cycle can then begin again.Melt water from Greenland’s ice sheet, which is low in salt content, reduces the density of the surface water in the North Atlantic. This could mean that the water masses will no longer sink deep enough to be transported back to the south. So far, there is no clear indication that this is happening, but model simulations show the AMOC could weaken by between 11 percent and 34 percent by the end of the century. This would lessen the warming in Europe, particularly in the British Isles and Scandinavia, but may also change wind circulation patterns, which could mean more severe storms in Europe.

14. Extreme hot weather is on the rise

Climate change is increasingly causing record- breaking high temperature and heatwaves. Between 1951 and 1980, less than 1 percent of the Earth’s land surface experienced unusually high summer temperatures. These hot-weather events, once very rare, occurred on approximately 10 percent of the Earth’s land surface in the period from 2001 to 2010. In addition, the average duration of the wildfire season increased by around 19 percent between 1979 and 2013 worldwide.

Cracked earth from extreme drought

15. Increased rainfall and flooding

Because higher temperatures allow the air to hold more water vapour, the water vapour content in the Earth’s atmosphere is increasing. Higher temperatures also allow more water to evaporate and thus higher precipitation levels may be expected. Water vapour does not usually fall as rain in the same place that it evaporated, and this, combined with shifting atmospheric circulation patterns, results in an increasingly uneven distribution of rainfall. Dry regions such as the subtropics are in many cases becoming even drier, while many humid regions like the mid-latitudes and tropics are becoming even wetter. At present, about 18 percent of the world’s heavy rainfall events on land can be attributed to global warming.

16. Drought risk is increasing

Global warming increases the localised evaporation of moisture from the soil, thus increasing the probability of droughts occurring both more quickly and more severely. Since the middle of the 20th century, the total area of arid land around the world has grown as a result of climate change. This is particularly the case in Africa, southern Europe, East and South-east Asia. This could increase the risk of droughts in the future.

17. Topical cyclones are becoming more severe

Tropical cyclones form over the ocean when the water temperature rises above 26°C, as they are powered by warm, humid air (latent heat). Climate change is causing the temperature of the sea surface to rise and consequently evaporation is increasing in turn, thus feeding more energy to the storms and increasing the chance of more severe storms occurring.

Close up picture of a Kākāpō

18. Eco-systems are shifting

Climate change is causing a shift in vegetation zones. The tree line in the northern hemisphere is moving northwards and reaching higher into the mountains. Climate zones have changed in much the same way. Between 1950 and 2010, roughly 5.7 percent of the Earth’s land surface shifted towards warmer and drier climate zones.

Animals and plants are well adapted to the climatic conditions of their habitat. There are three ways in which a species might respond to a changing climate:

  • They might adapt to the changes, coping very well and even increasing their numbers, as the bark beetle has done in many parts of Europe.
  • They might move their habitat, as species like certain kinds of butterfly do. Land animals and plants have been found to be moving to altitudes roughly 11m higher each decade, and travelling by around 17km further towards the poles.
  • They might be unable to adapt to the changes and may ultimately become extinct. The faster the changes take place, the greater the danger that animals and plants will not be able to adapt quickly enough to survive.

If one species changes, there can be repercussions for the entire ecosystem.

19. The impact on polar bears

There are currently an estimated 25,000 polar bears in the Arctic and subarctic regions. The increasing speed at which sea ice is melting in the Arctic summer is shortening the time that polar bears can use it as a platform to hunt seals. This reduced access to food can have a negative impact on the number of cubs they can birth and rear. The survival of adult polar bears is also directly threatened. While some polar bears have been observed eating berries and birds’ eggs in Canada, such alternative food sources are heavily dependent on local availability, and are not sufficient to meet polar bears’ nutritional requirements.

There is a great deal of uncertainty about how severe the impact of climate change will be on individual polar bear populations and over what time period. However, one thing is clear: if the sea ice retreats, the number of polar bears will decline.

Polar beer standing on thin ice

20. Coral reefs and bleaching

Tropical coral reefs are of crucial importance for humans. The abundance of fish they support serves as a food source, they protect coastlines against erosion by water and wind, and they are an important source of tourism for local economies. Algae that live on the corals and supply them with nutrients are responsible for their colour. Corals are coming under increasing stress from man-made warming, acidification and pollution of the oceans. If the stress level gets too high, the corals expel the algae and their white skeletons become visible (coral bleaching). This can lead to the corals dying because they are no longer sufficiently supplied with nutrients. In 2016, 93 percent of the reefs in the Great Barrier Reef in Australia were affected at times by coral bleaching, and in the shallow-water regions of the Pacific over half of the corals died between February and October 2016.

21. The threat to human health

Climate change is already affecting, directly or indirectly, the lives of all 7.8 billion people on Earth. The consequences of climate change affect human health in a variety of ways. Heat stress can exacerbate heart conditions and circulatory and respiratory diseases. High temperatures also boost the formation of ground-level ozone, which can compromise lung function. Increasingly frequent extreme weather events such as floods pose numerous risks to people. Heavy rainfall and flooding can cause microbial contamination of rivers and coastal waters, leading to an increased risk of outbreaks of waterborne infectious diseases.

22. The spread of vector-borne diseases

Organisms are referred to as “vectors” if they can transmit pathogens from an infected animal or person to other animals or people. Common examples include ticks and mosquitoes. As a result of globalisation and newly favourable climate conditions, the Asian tiger mosquito (Aedes albopictus) has managed to spread into parts of southern Europe over the past few decades. Climate change will also make European regions further to the north suitable for these mosquitoes. The tiger mosquito can transmit pathogens such as the dengue and chikungunya viruses.

23. Increased climate migration

Between 2008 and 2016, weather events – especially storms and floods – drove an average of 21.7 million people to migrate within their own country each year. In 2016, the figure was three times higher than the number of refugees from war and violence. Weather disasters also result in cross-border migration. The majority of those affected are poorer people, generally living in underdeveloped regions where the impact of climate change is particularly harsh. Such groups have generally contributed very little to climate change, yet they are most severely affected by its consequences.

24. Why we must all act now

Climate change is not some far-off reality. Many people and their livelihoods are already threatened by climate change. It has become clear that human greenhouse gas emissions are chiefly responsible for the increase in temperature since the start of industrialisation. Ironically, this is good news: it’s a reminder that we can influence how our climate develops in the future. We are not powerless against climate change.

 Small Gases, Big Effect: This is climate change by David Nelles and Christian Serrer
Extracted from Small Gases, Big Effect: This is climate change by David Nelles and Christian Serrer (Penguin, $21).


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