My degrees are in mathematics, and my research in the late 1960s and 1970s was on the mathematical theory of why we have strong weather fronts and on the basic mechanisms that lead to the behaviour of midlatitude low pressure systems. I was not working on climate change, but it became increasingly clear to me during this period that there was a strong scientific basis for concern over the likely warming of climate due to the ever-increasing emissions of carbon dioxide by human activities. I gave my first public talk on the matter in the mid 1980s: “Climate change, will we freeze or fry?” At that time there was publicity for a possible return to “an Ice Age”. However, in my talk I said that it was global warming we should be concerned with.

More than 30 years later, I am still giving public talks on climate change due to our greenhouse gas emissions. However, there are a number of big differences from the earlier time.

Years ago, the audience had no indication of rising temperatures and increased weather and climate extremes, but now they have experienced the changes, and have heard about them elsewhere. 30 years ago there was no indication that reducing greenhouse gas emissions was possible while maintaining or increasing the standard of living in a country. Now we have, or are developing, many of the technologies that make it a realistic possibility.

One of the things I have done, which I consider to have been very important, is that I was a member of the UK Climate Change Committee (CCC) for its first ten years. The CCC was set up to advise Government, monitor the UK performance and report to Parliament under the 2008 Climate Change Act. This Act was crucial for setting the legal framework for reducing UK emissions of greenhouse gases. 

Greenhouse gases in the atmosphere

The amount of carbon dioxide in the atmosphere has been measured directly in Hawaii since 1957. It is now measured more widely and is seen to vary little around the world. The Hawaiian record is shown in red in Figure 1. The black line shows a version that smooths out the well-understood annual cycle.  The amount (in parts per million of air) was about 315 in 1957 and has risen to about 415 in 2021. There is reliable information from gas bubbles trapped in ice that over the past million years it has varied between about 180 during the glacial periods to about 280 in the inter-glacial periods and that this would have been the approximate value before the 18th century. The subsequent rise of nearly 50% is due to human activity, and in particular the burning of fossil fuels – this is indicated by measurements of the isotopes of the gas and is consistent with the estimated magnitude of the emissions due to burning. 

Figure 1. Carbon dioxide measured in Hawaii since 1957. (Source: Sir Brian Hoskins)

Perturbations to the atmospheric CO2 content change it for a long period (compared with human time-scales) - it is estimated that if 100t of carbon dioxide is added to the atmosphere , an excess of about 15-40t will still be there in 100 years - the amount of extra carbon dioxide already added to the atmosphere is not going to disappear quickly. 

Laboratory experiments in London in 1860 showed that carbon dioxide and water vapour absorbed heat radiation with its relatively long wave-length but let through the light from the sun with its much shorter wave-length. This explained the notion raised 36 years earlier by the French mathematician Fourier that the atmosphere acted like a greenhouse, allowing the sun’s energy in, but reducing the heat loss from the Earth. Later, in 1896, a Swede called Arrhenius suggested that carbon dioxide levels in the atmosphere could be key in climate change.  

So 19th century physics leads to the idea  that the carbon dioxide already added to the atmosphere will have been warming our planet and that it will continue to do so while the greenhouse gas level in the atmosphere continues to rise. Given the long lifetime of carbon dioxide in the atmosphere, this means the temperature will continue to rise while human activities are adding carbon dioxide to the atmosphere. 

Observed changes in climate

Whether global temperatures have been rising is answered by the data given in Figure 2. This shows decadal and globally averaged temperatures from the middle of the 19th century. The results from 6 different institutions all show warming, and this is particularly striking in the past 50 years. Globally averaged temperatures are now about 1.2C above their pre-industrial value.

This is global warming, and its amount is consistent with the increase in greenhouse gases in the atmosphere, which itself is due to human activity. Nearly every region has warmed. The land has warmed more than the ocean, and the warming is largest in the high latitudes of the Northern Hemisphere.

Figure 2. Decadal global mean temperatures from 1850 to 2020.

From tidal gauges and more recently from satellites, we know that average sea level has risen by more than 20cm since the late 19th century. The recent rise has been at the rate of about 3½ cm per year. The rise is mainly a result of the small expansion of water with rising temperature. The melting of glaciers has also been important. More recently there has been a significant contribution from the decrease in the Greenland and West Antarctic ice sheets.

The warming Arctic has led to a decrease in sea ice volume and area. The ice grows through the winter to reach a maximum in March and then shrinks in the summer to reach a minimum in September. The decrease in area is particularly striking in the September minimum. Figure 3 shows the presence of sea ice as measured by satellite for 15 September 2020. Also indicated in the picture is the average position of the ice edge in the 30-year period up to 2010. The ice area varies from year to year, but the trend is such that it would lead to the sea ice almost  disappearing around the middle of this century. 

Figure 3. Ice in the Arctic on 15 September 2020 as given by satellite data.

The warming planet has been accompanied by many other changes in climate and weather events. In recent years the number of high temperature records has far out-numbered the number of cold records. Warm air can hold more water vapour than cold air. This effect is very strong: air that is 6°C warmer can hold about 50% more water, and it is usually found that it does. This means that the same rain storm could be expected to be 50% stronger in a 6°C warmer world. Consistent with this, heavy rainfall events have been observed to increase around much of the world.

The warm near surface waters of the tropical ocean are the energy source for tropical cyclones. As these waters warm, there is then a reason to think that tropical cyclones could become stronger. In agreement with this, there have been many record hurricanes (Atlantic) and typhoons (Pacific) in recent years, with record wind speeds on landfall and also intense cyclones in new regions. 

Future climate change and its impact

Computer models to simulate climate were originally based on weather forecast models, but now include more processes in the atmosphere, land surface, ocean and ice. At their heart they have Newton’s Laws of motion and the equations of thermodynamics. Complex climate models have been produced  by a number of different centres around the world, and there are numerous simpler climate models. They are all continually evaluated using past and near present climate data, which helps to give confidence using them to study possible future climates. 

To run the climate models for the future, scenarios for greenhouse gases and other relevant aspects of human activities need to be chosen.  Figure 4, taken from the 2013 Assessment of the Inter-Governmental Panel for Climate Change (IPCC) shows a collection of the results for two emission scenarios.

The upper curve is for greenhouse gas emissions continuing to grow and the lower curve is for emissions being drastically reduced. For the high scenario, the global temperature increase by 2100 is likely to be in the range 4 to 5.5°C, whereas for the low scenario the likely range is 1.5 to 2°C.

Figure 4. Climate model projections of global temperatures up to 2100 for high and low greenhouse gas emission scenarios. A range of the model results and a mean is shown for each of the scenarios. For changes from the pre-industrial period, 0.6°C should be added to the numbers. (Source: IPCC 2013)

Considering the upper scenario in 2100, the change in temperature over land would generally be more than 5°C and the rise would be much larger in northern high latitudes, being as much as 12°C in winter. The uneven warming would mean that weather, which feeds off temperature contrasts, would be different. Average rainfall would change in many regions, and the rain would fall in heavier  storms. The strongest typhoons and hurricanes could be considerably stronger, and their pathways could change. Sea level would probably rise about 1m.

The impact on human activity of the change in climate associated with the upper scenario would be immense.

In the hottest regions out door activity in the day would be almost impossible. River flooding and water availability would be problems. Coastal flooding would impact a significant number of cities and regions. Agriculture would be severely impacted. There would probably be large migrations of peoples from regions in which climate change has made life unliveable. The lesson of history is that such stresses would lead to conflict - in western military circles climate change is seen as the biggest security threat.

In the lower scenario, the impacts are still significant, but in most regions of the world it is likely to be possible to adapt to the slower and smaller changes in climate.

When considering the possible impacts of climate change and adapting to them, every country is concerned to have detailed information on the possible change in its own country. Taiwan is fortunate that scientists in Academia Sinica have been working on  such detailed projections for some years.

Mitigating climate change

Under the auspices of the UN, the countries of the world meet to discuss action on climate change. At  “COP21” in 2015 the Paris Agreement emerged. In this, the countries of the world decided that the change in global temperature should be limited to below 2°C and preferably nearer 1.5°C. The lower scenario discussed above is in this range.

The Nationally Determined Contributions (NDCs) for 2030 emissions offered by the countries in Paris added up to give 3°C or more, but it is hoped that, in the delayed COP26 in Glasgow later this year, the NDCs will be tightened to be closer to consistency with the Paris targets. There are hopeful signs in that the UK and EU have now promised 68% and 55% reductions from 1990 levels, and the US is now on board with a 50% reduction from 2005 levels. All agree that there must be net zero greenhouse gas emissions by 2050, with any residual greenhouse gas emissions compensated by carbon dioxide removal through natural or technological means.

These targets have been made possible by the amazing technological developments - in the power sector through wind and solar power and batteries, electric vehicles, production and use of “green hydrogen”, and many new manufacturing processes. It is clear that we are in the initial stages of a new industrial revolution. This is where the new economic opportunities are to be found, where the big investors are now moving, and where the jobs of the future will be.

Businesses will feel the impact of climate change through changes in their markets, impacts on their supply lines, the regulations they face, the greener inclinations of investors, and the expectations of  employees and customers. The uncertainties they face will depend on whether the challenge of climate change is taken on board by governments and by the businesses themselves.

Concluding Comments

It is to be welcomed that in April President Tsai Ing-wen announced that Taiwan is charting a path to net zero emissions by 2050. As I did in my 2019 visit to Taiwan, I recommend consideration of aspects of the UK Climate Change Act, with its framework of short- and long-term legally-binding targets, and the creation of an advisory and monitoring body like the CCC.

Climate change is a big challenge to our species. However, by tackling it we are opening up a new world with many co-benefits: better air quality and health, stimulus for economies and jobs and better paths to development for poorer countries.

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About the author:

Sir Brian Hoskins was the Founding Director of the Grantham Institute for Climate Change and the Environment, and is now its Chair. He has been a Professor in Meteorology at the University of Reading for more than 35 years, and now fills the position on a part-time basis. For 10 years he also held a Royal Society Professorship. His research is in weather and climate, in particular the understanding of atmospheric motion on all scales.

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