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Climate change

Article curated by Ginny Smith

Scientists agree that human activities are causing climate change, but the finer details are still unknown. By how much will temperatures rise if it continues at the current rate? And what impact will this have on our weather, other animals, and human lives? Unfortunately, predicting these factors is extremely difficult, and there is still much we don't know about the future of our planet.

Entering the unknown - with greenhouse gas emissions at record heights, what will the effect be on our Earth? Image credit: Public domain

Global Warming

The Earth is a complex ecosystem, held in a fine balance that allows life to thrive, and offsetting this balance can have massive repercussions. A relatively small change in temperature can have big knock-on effects, and a large change could result in an uninhabitable Earth.

Heat and light from the sun is vital, but too much of it would be catastrophic. Our Earth is protected from the Sun's intensity by its distance, and by clouds and ice which reflect some of the sun's heat back. When sunlight reaches the Earth’s atmosphere, some of it gets reflected and some of it passes through and is absorbed by the Earth’s surface. Cities and roads are darker than forests and fields, and absorb more of the Sun’s energy. As the Earth warms up, it also radiates energy, and the amount of this re-radiated heat that escapes into space also depends on many factors, such as the constitution of our atmosphere.

If more energy is absorbed than emitted, the Earth warms until it radiates more energy to balance off, or until some other factor changes and reduces the incoming energy. If less energy is absorbed than emitted, the Earth cools down. The Earth is currently warming due to just such an imbalance - the absorbed solar energy exceeds the emitted thermal energy by just 0.4%.

A large factor when considering global warming is the infamous ‘greenhouse effect’. The so-called ‘Greenhouse Gases’, predominantly but not exclusively CO2, absorb the radiation and re-emit it in all directions. This causes more heat to be trapped within the atmosphere and hence has a general warming effect.

But while this much is agreed on by the majority of the scientific community, the details of how much warming will take place, and how that will impact life on Earth are far from clear.These discrepancies arise because creating a model of our changing environment is extremely difficult given the many variables and unknowns. The exact details of how much warming will take place, and how that will impact life on Earth are far from clear.

wikimedia commons
The Greenhouse effect - Heat emitted and reflected by the Earth Image credit: Public domain

Lessons From History

Ice ages are periods of time when glaciers cover a large areas of the surface of the Earth, and are otherwise known as “glacial periods”. While temperatures during these periods still fluctuate, the glaciers remain features of the landscape until the ice age comes to an end. We know that they have previously occurred, and can get an idea of their conditions due to plentiful evidence, including analysis and comparison of polar ice caps to other geological features and examination of fossils for signs of adaptations to colder climates.

Doubts arise, however, when attempting to determine the conditions required for an ice age to occur, candidates for which appear many and varied. To list just a few; changes in the Earth’s tilt and orbit, atmospheric conditions, volcanism, the sun’s activity and the motion of tectonic plates. This leaves us with an incredibly complex model. While we know all these factors can contribute to an ice age era, we don’t know if all are necessary and to what degree. Developing a means of replicating and analysing the conditions would be the most conclusive way to discover which factors have the greatest effect in altering the Earth’s temperature.


Some scientists even argue that there were periods in the Earth's history where it was completely covered in ice - the so-called "Snowball Earth". The average global temperature would have dropped to -50C as the ice and snow reflected away a large proportion of the sun's radiation. It is thought that these periods were partially caused by a decrease in greenhouse gasses, as the activity of CO2 consuming microbes increased due to ideal conditions. As the planet cooled, the activity of these microbes would decrease again, allowing greenhouse gasses to build up once more, and the snowball Earth to end. But while this might have contributed to these eras, it is not enough to explain the Snowball Earth effect completely. It is likely a number of factors coincided to cause it, but for now how exactly the snowball Earth happened, or whether it even did, is still under debate.

Neethis via Celestia Motherhole (public domain)
Snowball Earth - Could the Earth ever have been completely covered in ice? Image credit: Public domain

A typical ice age lasts 400,000 years. These are punctuated by interglacial periods, warmer stages, which usually last about 11,500 years. Currently we are 12,000 years into an interglacial period, which could be taken as implying that another ice age is imminent, but scientists aren’t so sure…

We have cause to believe this interglacial period will be longer because the Earth’s tilt and its orbit are about 10,000 years out of phase. The Earth’s orbit isn’t a perfect circle, we’re sometimes slightly closer to the Sun and sometimes further away. The tilt of the Earth gives us seasons, and we’re closest to the Sun during the northern hemisphere’s winter, and the southern hemisphere’s summer. This is important, because there’s more land in the north, and more water in the south. Although land heats and cools more quickly than water, water retains more heat than land does. So if we were closer to the Sun during the northern hemisphere’s summer, the Earth would be cooler.

When the temperature decreases, ice sheets cover more of the surface of the Earth. This in turn means more sunlight is also being reflected by the ice back into space, amplifying the cold spell this phenomenon instigates. Given that the tilt and orbit are so out of phase, their cumulative effect is far weaker, hence scientists believe this alteration in conditions might elongate this warm phase. The last interglacial period that occurred under similar conditions lasted 30,000 years, so we still have a while to go.

The human race is adding an unpredictable variable into the mix, with the amount of CO2 and greenhouse gases released into the atmosphere causing a progressive global warming effect. This warming process may be enough to counteract the cooling effect leading up to an ice age. Consequentially we are entering unknown territory. The glacial-interglacial pattern may well be stopped in it’s track due to too much human interference.


The Present Day

It’s widely known that humans are producing huge amounts of CO2, and that the majority of scientists agree that this is contributing to climate change. But what exactly happens to the CO2 that we release isn't fully understood. NASA launched the Orbiting Carbon Observatory-2 satellite in 2014 to help map and sample CO2 levels and, hopefully, to find out.

We know that there are natural 'carbon sinks' in the world - areas that absorb more carbon than they release. Examples of these include bodies of water and plants photosynthesising. Unfortunately, little is known about these sinks - how much CO2 can they mop up? And what will happen when they are full? Using the data collected by this mission scientists hope to find the exact location of these sinks to allow them to investigate them further. Understanding how these sinks work will help to predict the future of climate change, and may even give clues to how we could build artificial sinks to mitigate our own impacts on the environment.

We know that there are natural 'carbon sinks' in the world - areas that absorb more carbon than they release. Examples of these include bodies of water and plants photosynthesising. Unfortunately, little is known about these sinks - how much CO2 can they mop up? And what will happen when they are full? Using the data collected by this mission scientists hope to find the exact location of these sinks to allow them to investigate them further. Understanding how these sinks work will help to predict the future of climate change, and may even give clues to how we could build artificial sinks to mitigate our own impacts on the environment.


There has recently been some debate over whether global warming has started slowing down after NASA conducted a study of the temperature of the deep ocean. Using satellites, information was collected from 2005 - 2013 from ocean depths below 1,995m[3]. The data demonstrated the temperature had not increased notably over that time, despite the effects of global warming still progressing.

Greenhouse gases are still progressively accumulating in the atmosphere, but while surface temperatures and sea levels are still rising, they are not doing so at the rate believed to correspond to the the amount gases released.

So with both the surface and deep ocean not behaving as expected with respect to temperature, we are left asking - where is the missing heat going?


A number of previously unseen or changing atmospheric phenomena may be a result of the changing temperatures. One of these is the appearance of Polar Mesospheric Clouds. These "noctilucent," or night shining, clouds are so high up they are illuminated by the sun even when it is below the horizon, giving them an eerie glow. They form over both poles during the summer, and have been observed since 1885, but their brightness and frequency seems to be increasing. They are also being seen at lower latitudes. Although we don't know how or why they form, it is thought that their increase could be linked to differences in atmospheric temperature due to climate change.


What effects will climate change have?

We don't know exactly what will happen if climate change continues unchecked, but one problem that seems unavoidable is the rise in sea levels. As temperatures rise, ice will melt and the water in the sea itself will expand. This could devastate coastal populations of humans as well as animals and plants.

However, we don't yet know how big a problem rising sea levels will be, as there are so many factors to take into account. The rate the ice melts and differences in evaporation and rainfall will have an impact, as will changes in the atmosphere's ability to hold water. While scientists are attempting to model these changes the number of different factors involved, and the fact that they are all interrelated, makes this a very challenging task.

wikimedia commons
Global warming has its consequences. Sea levels are rising and soon coastal habitats will be lost for animals and humans alike. Image credit: wikimedia commons 

Another relevant question is “can animal species adapt to cope with a change in conditions”? Different animals react very differently to changes in their habitat, so it is impossible to predict how every species will cope. Those that are likely to be hardest hit are the ones living in areas with very little temperature fluctuation, such as the poles or the tropics. These creatures are perfectly adapted for the temperature they live in, and even small changes could prove devastating for them.

A study on evolution and heat tolerance was carried out in 2011 on a tiny sea creature, commonly found in tide pools, known as a Tigriopus Californicus. While the species illustrated a large variation in heat tolerance, due to living in different in different locations before the study, the Tigriopus Californicus from the same environment demonstrated a maximum tolerance of half a degree Celsius warmer over ten generations, with most floundering before that point[1].

It is believed that many species are already at their upper limit of heat tolerance, and it seems likely that in many situations evolution and natural selection will not outrun climate change. If even one species nears extinction it can unbalance the ecology completely, causing a chain reaction and affecting multiple species that were reliant in some respect on the now extinct species, whether directly or indirectly.

Heat related deaths would increase as a direct result of global warming2, but the physiology of a healthy human could handle a slight increase in temperature. Whether civilisation could cope with the changes this increase may incur to our environment however, is up for debate.

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From an economic perspective, global warming is predicted to have a direct economic cost , although working out what that might be is a huge task. An increase in droughts and flooding due to more extreme weather conditions, along with damage caused by sea levels rising, and other problems associated with the rising temperatures are could cost $200bn for the EU alone if global temperatures increase by 3.5 degrees[2], as is currently expected. Heat-related deaths could also reach about 200 000 a year.

Giuliamar (CC0 Public Domain via Pixabay)
Rain Image credit: Public domain

So what can we do to prevent the possible devastation climate change could cause? One important factor is to cut our carbon emissions. Burning of fossil fuels accounts for the majority of our CO2 emissions, so finding a replacement would be a huge step forward. One possibility would be using hydrogen. Hydrogen is an effective fuel, but most methods of production are very expensive, inefficient and/or require the use of fossil fuels.

Now scientists at the University of Virginia have created a combination of enzymes which can break down plants, including waste food, to produce hydrogen. This happens at relatively low temperatures, so shouldn't be as costly as current methods.

While this is exciting research, the process still needs to be scaled up, and its efficiency maximised, before it can be brought onto the market. The safety problems of using hydrogen (which is extremely explosive) as a fuel also need to be tackled. But who knows? In the future we may be stopping by the side of the road to stock up on sugar, rather than petrol.


This article was written by the Things We Don’t Know editorial team, with contributions from Ed Trollope, Jon Cheyne, Cait Percy, Johanna Blee, Grace Mason-Jarrett, and Holly Godwin.

why don’t all references have links?

[1] Grosberg, R.K. Kelly, M.W. Sanford, E. “Limited potential for adaptation to climate change in a broadly distributed marine crustacean” Proceedings of the Royal Society B: Biological Sciences, 2011
[2] Graeber, D.J. “EU wary of economic hit from climate change” UPI, 2014
[3] Rasmussen, C. “NASA Study Finds Earth’s Ocean Abyss Has Not Warmed” JET Propulsion Laboratory, California Institute of Technology, 2014

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