What is Climate Change?

“[The unchecked burning of fossil fuels] would have a sort of greenhouse effect”, and “The net result is the greenhouse becomes a sort of hot-house.” Alexander Graham Bell, 1917

Bell went on to also advocate the use of alternate energy sources, such as solar energy.

Zero Chippenham member: “Climate change is really the trigger that got me personally working towards sustainability, examining everything we do as a business. When the Intergovernmental Panel on Climate Change (IPCC) interim report landed in 2018 (3) and received wide scale publicity it was a real shock. Though I had heard of global warming and Climate Change, I wasn’t aware of just how severe and far reaching the effects were likely to be, and what little time we had to act.”

The Science of Climate Change

Climate Variation in the last two million years
The following information is derived from a short course by Professor Dan Charman – University of Exeter.
We’re all perhaps familiar with the concepts of Ice Ages and some of the dramatic climate variations that have occurred in the last two million years. The main changes over thousands of years such as Ice ages are predictable and are caused by variations in the shape of the Earth’s orbit and the angle and location of its axis.
Serbian scientist Milutin Milankovitch proposed that the changes in the intensity of solar radiation received by the Earth were affected by three fundamental factors. The first of these is called eccentricity, a period of about 100,000 years, in which the nearly circular orbit of the Earth, changes into a more elliptical orbit. When the orbit is circular, the distribution of energy is equal throughout the year. When it is fully elliptical, the Earth is slightly close to the sun sometimes, so it receives more energy at that time of the year.
The second factor is called obliquity, a period of about 41,000 years, when the Earth’s axis tilt varies between 21.5 and 24.5 degrees. This also changes the distribution of solar radiation on the planet.
The final factor is called precession, a period of approximately 23,000 years, where the Earth’s axis wobbles like a spinning top. As it wobbles, the timing of the seasons changes. For example, 11,000 years ago, the Northern Hemisphere was tilted toward the sun at the same time as the Earth is at its closest point to the sun.

This meant that there was a greater difference between summer and winter causing much more seasonal climates.
If the changes in the Earth’s orbit are totally predictable, why can’t we predict natural variability precisely? Well that’s due to the interaction of feedback mechanisms in the climate system we’ll explore next.

As you may have seen on nature programmes exploring the polar regions reducing sea ice cover exposing the dark ocean underneath causes the Earth to absorb a lot more heat radiation.

Overall, the Earth reflects about 30% of the sunlight that reaches it from space. In other words, it has an albedo of around 0.3. If it was just down to the absorption of the sunlight and heat that reaches the Earth, we would be very cold indeed, as our planet would have an average temperature of 18 degrees centigrade below zero!

But due to the blanket of gases in the Earth’s atmosphere the surface is warmed by 33 degrees to an average temperature of 15 degrees centigrade.
So we do need a certain amount of greenhouse gasses in the atmosphere.

What is Climate?
The following information comes from the UK Met Office.
Firstly let’s clarify the often asked question – What is the difference between weather and climate?
“Weather is the elements we see daily such as temperature, rain and wind. These can change by hour and day by day. Climate on the other hand looks at how the weather changes over long periods of time. Typically around 30 years. Scientists have been able to define climate zones around the world.

Here in the UK we have a temperate climate that is neither especially hot nor cold wet nor dry when compared to other climates. Ours is a very different climate to that in the Sahara for example which is known as arid because throughout the year the weather is dry and hot. Scientists have to look at how the atmosphere interacts with the oceans, ice sheets, land masses and vegetation. These different interactions create a climate system and these interactions as well as the composition of the atmosphere itself create a very complex system.”
So What are the Climate Systems?
Professor Tim Lenton of the University of Exeter gives an excellent explanation on this….
The Climate is conceptualised as a system that encompasses five key components
– The Atmosphere
– The Hydrosphere– primarily the oceans, but also fresh water, rivers, lakes, and groundwater
– The Biosphere – all the living things in soils
– The Cryosphere – ice sheets, sea ice, and mountain glaciers
– The Lithosphere – the surface of the Earth’s crust.

If we look closer there are a series of cycles that form the links and interactions between the components that form the climate system.
The water cycle.
Solar radiation causes water to evaporate from the surfaces of lakes, rivers, and the oceans. From the biosphere water evaporates and transpires from green plants. Water vapour condenses in the atmosphere to form clouds, and returns to the surface through precipitation, rain and snow fall. On reaching the surface, water returns to the hydrosphere. If it is frozen as snow, it can enter the cryosphere.

Sunlight on the cryosphere can melt snow and ice or transform it directly into vapour. The key take away is that the water cycle is influenced by a wide variety of factors that can be changed by human activity.

Feedback effects
There are a number of feedbacks that operate in the dynamics of the climate system. Cycles that connect components of the climate system create feedback loops, that is closed loops of cause and effect. As a former engineer I’m very familiar with feedback loops in electrical control systems, be it a simple thermostat to control temperature, or a more complex system to control the power transmission of a mobile phone mast.
The climate system has multiple feedbacks acting to regulate the climate towards a particular state.
There are three key Climate feedback mechanisms
– Water vapour feedback
– Ice albedo feedback
– Radiation feedback.

Ice albedo feedback.
An area of ocean that is covered by sea ice such as the Arctic will reflect back much of the solar radiation due to the highly reflective ice, which we say has a high albedo. The Dark ocean surface, on the other hand tends to absorb more than it reflects, because it has a low albedo. So as the ice melts we have a gradually less reflective surface and so we absorb more heat reinforcing the melting. Again a positive feedback loop.

A warmer atmosphere holds more moisture and it appears that globally averaged precipitation may have increased over the last century. Extreme rainfall events have increased over many land areas. However the increase isn’t equally spread around the world and regions such as the Mediterranean, have been getting drier. Global average precipitation is projected to increase, with wet regions getting wetter and some dry regions becoming drier.
The IPCC 2013 summary says
Changes in the global water cycle in response to the warming over the 21st century will not be uniform. The contrast in precipitation between wet and dry regions and between wet and dry seasons will increase, although there may be regional exceptions.

Sea Ice

Arctic sea-ice extent has declined by 0.45-0.51 million km2 per decade, and the corresponding ice albedo feedback is a major reason why the Arctic is warming roughly twice as fast as the global average. In contrast, Antarctic sea-ice extent was increasing at 0.13-0.20 million km2 per decade, linked to changing wind patterns over the Southern Ocean. However, global sea-ice extent in 2016 was the lowest on record, with the November extent being 2 million km2 less than the November 2015 extent. – University of Exeter

Tipping Points
As we have evolved as humans (i’m assuming we’re all human reading this!) over the last 10,000 years we’ve tended to experience the world as a series of linear increments. This can lead us into the false sense of security that Climate change is a gradually incrementing change that we can offset by gradually decreasing our carbon dependency.
However the Climate is a complex system and is unlikely to act in this way.
Professor Tim Lenton – University of Exeter and the Potsdam Institute for Climate Impact Research (PIK) have been key in identifying potential Climate tipping points in the biosphere (2).
Here i’ll briefly look at Tim’s research on three potential Climate tipping points:-
– Arctic Sea-ice Loss
– Dieback of the Amazon Rainforest
– Ocean Current Circulation Systems
Artic Sea Ice Loss
The positive feedback effect around the melting of sea-ice in the Arctic means that this region is warming at more than twice the global average rate. This could lead to a tipping point that leads to the Arctic becoming free of sea-ice in summer. While this may have a positive effect of opening up shipping routes the impacts could have global consequences.
A transition to a system with much less sea-ice is already underway.

Greenland Ice Sheet

Ice sheets are much slower systems to the sea ice that take longer to melt. The majority of the Greenland ice sheet is resting on land and so is only affected by the ocean near the coasts. It could still pass a tipping point where it retreats completely on to land, leading to a 15% loss of the ice sheet – equivalent to 1m of global sea-level rise. Evidence from monitoring the retreat of glaciers around the coasts suggests this tipping point may already have been passed.
There is uncertainty as to where the tipping point lies for the irreversible melt of the whole ice sheet. Estimates range from a high probability of loss at 4°C to a much closer estimation of 0.7-1.7°C global warming.

Collapse of the West Antarctic Ice Sheet (WAIS)
Large parts of the WAIS are below sea-level. If a positive feedback is triggered resulting in retreat of the ice, it could result in the collapse of the ice sheet. Research shows this has happened before in past warm intervals. Major ice shelves are thought to need approximately 5˚C of warming to reach a critical threshold of melting, while the entire WAIS could require up to 8˚C.
“However, there is worrying evidence that part of the WAIS that drains into the Amundsen Sea is already in irreversible retreat and ultimately represents over 1m of sea level rise.
A further sign that the WAIS could be reaching an early tipping point would be the collapse of ice shelves. The most northerly of these are the Larsen ice shelves on the Antarctic Peninsula. Larsen A (the most northerly) collapsed in the mid-1990s. Larsen B – which has remained stable for the last 10,000 years – broke up rapidly in the summer of 2002. Larsen C is significantly larger than Larsen A and B, and in July 2017 an iceberg twice the size of Luxembourg calved from its front. This could be an early signal of much worse to come, but could also be part of a natural process of mass loss in this ice shelf.” -Professor Tim Lenton University of Exeter

Amazon Dieback
An astonishing 25% of global biodiversity is contained within the Amazon Rainforest making it one of the most ecologically important regions on Earth. The Amazon plays an important global role in carbon and nutrient cycling. It helps create local, regional and even global climate stability.
It’s pretty shocking therefore to think that a climate tipping point may be unfolding. Droughts in 2005, 2010 and 2015/6 could be a clue of impending Amazon dieback.
“Dieback is the process of death in trees or other vegetation. This can be due to a number of pressures, internal and external, including drought, disease or an unfavourable environment.”
The pressures on the Amazon and other tropical forests such as the Makira in Madagascar are many and could lead to dieback.
Human activity in the Amazon region is increasingand protective legislation is thin. Populist leaders are elected who’s priority is not to protect the rainforest. Deforestation and an increase in the number of forest fires across the region contribute to dieback.
Climate change is resulting in shifting rainfall patterns that could lead to the forest becoming Savannah.
Savannahs store less carbon than tropical rainforests, so the transition of the ecosystem to this new stable state would release carbon to the atmosphere and trigger extinctions. Savannah and seasonal forests cope better with dry conditions and more resillient to forest fires. This is what makes this new system a stable state.
“With fewer trees, there will be less forest transpiration, resulting in decreased surface cooling and higher regional air temperatures. Dieback of the Amazon rainforest would, therefore, exacerbate the impacts of climate change that are already being felt in this region.” – Professor Tim Lenton
A tipping point is predicted at temperature rises of 3-4˚C from pre-industrial levels (we’ve already reached 1˚C). However there are large uncertainties in the model predictions of rainfall changes across the basin, with models not fully capturing the complex microclimates that the rainforest produces.

Ocean Current Circulation Systems
“Circulation Systems control the movement of thermal energy (heat) around the world. This takes place in the atmosphere, through winds, and in the ocean.” – Tim Lenton University of Exeter

Atlantic Thermohaline Circulation (THC)
The deep, cold, salty water in the North Atlantic sinks as it becomes more dense, from the cooler temperatures and increased salinity. This is a delicate balance driving global ocean current circulation. Should an Ice sheets like the Greenland Ice Sheet melt it releases freshwater into the North Atlantic that has the potential to overturn circulation of this ocean current.

El Nino Southern Oscillation (ENSO)
The El Niño / La Niña cycle is a natural cyclic phenomenon in the Pacific Ocean that occurs naturally roughly every 5 years. Climate change is amplifying the cycle. The 2015-16 El Niño was one of the strongest on record, following an exceptionally strong 1998 El Niño. It caused a global coral bleaching events including those witnessed by ourself in North-West Madagascar. It also caused droughts, hurricanes and significant flooding across the world. One of the controlling factors in the ENSO cycle is the thermocline of the ocean – a dividing layer that separates deep and surface oceans. As the surface oceans absorbs more heat due to climate change the thermocline gets sharper and steeper. Though there is some uncertainty the latest climate models predict more extreme El nino / La nina events as the century progresses.

Doesn’t this sound like science-fiction?
“The sensitivity of ocean circulation systems to climate change is poorly understood. We think that the rate at which change is occuring today will make tipping points more likely in the future. But those tipping points in the Earth’s circulation systems could still require another 3˚C of warming. Nevertheless, even modest changes to these enormous systems have global impacts that we are already seeing today.” – Professor Tim Lenton University of Exeter

1. https://www.pnas.org/content/106/13/5041.full

2. Tipping Elements in the Earth’s Climate system – Professor Tim Lenton https://www.pnas.org/content/105/6/1786.full

3. Intergovernmental Panel on Climate Change report Global warming of 1.5 degrees C https://report.ipcc.ch/sr15/pdf/sr15_spm_final.pdf