What Are The Causes And Effects Of Climate Change?

Climates can change for a variety of reasons. The natural factors which affect climate change work over tens of thousands of years. Today we are experiencing rapid climate change caused by human activities that increase the quantity of greenhouse gases in the atmosphere, leading to rising temperatures, melting ice, rising sea levels, and extreme weather events. This affects both human populations and entire ecosystems, as well as having a significant impact on businesses. Barbara Scherrer and Thomas Eldridge, two of our meteorologists, provide further insight on climate change in this interview.

What is the climate and how does it change? What caused climate change in the past, and why is the climate changing today?

Meteorologists define the climate as the long-term average of the weather; conversely, the weather is defined as the short term fluctuations of the mean atmospheric conditions.

The climate is the way that it is because of the Earth’s position in the solar system; the composition of the Earth’s atmosphere and surface; and the distribution of landmasses and mountains. These are the factors which influence the amount of energy stored within the Earth’s climate system, and the way in which this energy is distributed from the equator to the rest of the planet, which is essentially what drives all weather. If the planet were perfectly symmetrical, and the incoming radiation perfectly constant, then a steady state would be reached, and weather would not exist.

Climate can change if any of these factors change. In the distant past, the Earth has been at times closer to and further from the sun, and at times more or less tilted relative to its orbital plane. These variations - called ‘Milankovitch cycles’ - have been responsible for ice ages in the past, but take place over tens if not hundreds of thousands of years. Other natural factors include fluctuations in solar activity, and changes in concentrations of ‘greenhouse gases’.

What are greenhouse gases and where do they come from?

Yes, you read that right - the greenhouse effect is a natural effect! It is the name we give to a physical process by which the atmosphere preferentially lets radiation from outside of the Earth reach the surface, whilst not letting the radiation which leaves the surface escape. Greenhouse gases include CO2, methane, nitrous oxide, and water vapour. These gases have existed in our atmosphere for billions of years, and fluctuate naturally due to plant respiration, decomposition, and ocean release.

However, human activity since the start of the industrial revolution has rapidly increased the fraction of our atmosphere which is composed of greenhouse gases. The burning of fossil fuels like coal, oil, and natural gas, for energy production and heating in industrial processes, releases carbon dioxide.

Agriculture is also a major source of methane and nitrous oxide emissions, mostly due to ruminant livestock digestion processes and fertilisers.

This all causes more heat to be trapped in the Earth’s climate system, which leads to the intensification of the general circulation of the atmosphere and oceans, and consequently more violent weather.

How do greenhouse gases trap heat?

The specifics of how the greenhouse effect works are pretty technical. All objects in the universe - even you and me - emit radiation. It’s just that this is not always obvious, because most objects are not hot enough to emit visible light. You can get an intuitive feel for this if you think about viewing the world through a thermal camera (an instrument which can sense infra-red radiation and converts this signal to colours you can see).

All objects also absorb radiation. To be in ‘thermal equilibrium’ (neither heating up nor cooling down), an object has to emit the same amount of radiation it absorbs. However, in general, an object will not emit this radiation at the same temperature, so they will emit a different kind of radiation. The sun has a temperature of approximately 5600 K, which is hot enough to emit visible light; the Earth absorbs this radiation, but has a temperature of 290 K, corresponding to infra-red. (Note that reflection is not the same as absorption and re-emission - the Earth does reflect a portion of the incoming solar radiation, which is why we can see things in the daylight, but this energy is not generated by the Earth.)

Now for the complicated bit.

Unlike the Earth’s surface, the atmosphere is not solid. This means that it is easier for radiation to pass through it without being absorbed. But the gases prefers to absorb radiation at certain wavelengths. (The reason for all this is to do with the energy that can be stored in different ‘degrees of freedom’ within bound molecules: solids, which exist in crystalline lattices, have a great many ways of absorbing energy; gases only have a few - we can see which ones when we look at the ‘spectral lines’ which are absent when examining the radiation which has passed through a sample of gas.) Greenhouse gases are gases with a particular pair of properties: first, they allow incoming solar radiation to pass through relatively unimpeded; and then, when the Earth absorbs this radiation and re-emits it at thermal infrared wavelengths, they themselves absorb the radiation. You can think of greenhouse gases as a kind of one-way-mirror for heat.

What are the ecological effects of climate change?

The rate at which this is happening is a major concern. Yes, climate has changed in the past, but as far as we can tell from the fossil record, this has always led to mass extinction events, and the rate of climate change today is much more rapid than the natural variations we know about from natural history. To survive whilst the climate changes requires that animals evolve and migrate to adapt to the new conditions, and these processes take millenia. The concern today is that many species will fail to adapt, will go extinct, and that this will cause total ecological collapse. The planet’s ecosystem has always been in delicate balance - little disruptions can be compensated, but effects as large as those we’re seeing today will be catastrophic.

How to measure climate change?

To measure the causes of climate change, we measure the concentration of greenhouse gases in the atmosphere. We do this via spectroscopy: we capture random samples of the atmosphere, shine light through the sample, and observe the spectral absorption of the sample. We can compare this against the atmosphere from the past because samples of the atmosphere as it was then have been captured in air bubbles in ancient ice. By drilling deep holes in large ice sheets, such as those found in Greenland and Antarctica, we can see how greenhouse gas concentrations have varied over a period of almost a million years.

In terms of effects, the most direct consequence of climate change is the increase in global temperature. Of course, the temperature can easily be measured using a thermometer, but it’s important to remember that local fluctuations due to the weather are to be expected everywhere. To measure the climate, we need to take the temperature of the entire planet. This can be done at well distributed ground based observatories, but additionally today we can measure the temperature of the Earth from space using satellites.

The impact on the Earth’s climate system which is caused by climate change is also visible all around us. Glaciers are retreating; ice caps melting; previously arable lands turning into deserts; sea levels are rising and extreme weather events are becoming more frequent. However the links between global temperature and the local climate are complicated, so whilst we can make predictions about what may happen on regional scales, and can measure these outcomes, we rarely use them to measure the rate of climate change explicitly.

What are the most dangerous effects of climate change?

In the long term, the most dangerous consequence will be the ecological collapse likely to occur as more and more species struggle to adapt and are removed from the ecosystem. Although humans, due to their ability to create technology to fill the gaps left by nature, will be insulated from this for a while, there will come a time when even our food chain is disrupted. At this point, quite simply, there will not be enough to go around, and large portions of the population will starve.

In the shorter term though, the increased frequency of extreme weather events is already wreaking havoc across the globe. The frequency and intensity of heavy precipitation events has increased, as warmer air can hold more water vapour. Forest fires - themselves an important natural event - are now difficult to control, burning further and for longer than they once did. And for complex (although well understood) reasons to do with the global circulation, intense cyclones, including hurricanes, are becoming more common.

As much as humans are more adaptable (at least on shorter timescales) than other animals, we too have developed most of our infrastructure with the tacit understanding that the climate is something we can count on staying the same, and we are seeing the implications of this today, as more and more cities are inundated by floodwater, and more and more countrysides are becoming dry and barren, forcing populations to move.

How does climate change affect businesses?

Much as our infrastructure has historically assumed that the climate is a constant, so have businesses small and large. The weather of the future will be different to the weather of today, and if your business is impacted by the weather, you can expect business as usual to be disrupted to varying degrees.

Consumer behaviour changes with the weather – with more people staying indoors on a miserable day and, conversely, venturing out when the weather is warm. This has impacts on retail, leisure, and also domestic heating and electricity usage.

Some other industries are more likely to be directly affected by climate change. We’ve already mentioned that agriculture will be heavily impacted as many areas become barren. Additionally, aviation and logistics will have to deal with more adverse weather conditions when planning routes; and infrastructure, planning and insurance will all have to deal with more extreme weather and the damage it can cause.

There are two axes along which we can work against climate change. One of these is adaptation, and climate change may create new business opportunities for those interested in building new infrastructure to defend against extreme weather, and produce new agricultural methods in order to provide food for a growing population. Adaptation is required, as climate change has already begun and some effects will take a long time to reverse, if that is even possible.

The other axis though is fundamentally more important. Mitigation has to be the priority, because as much as we as humans may to a limited extent be able to adapt to climate change, the rest of the inhabitants of planet Earth will find this much more challenging, and there will come a time when humans will not be able to survive by themselves. Businesses that can make a difference here are those which can fulfil the demands of society without spewing more greenhouse gases into the atmosphere, and include renewable energies, electric vehicles and sustainable agriculture.