+4 °C: Tens of millions become refugees as rising waters threaten the Nile Delta and low-lying Bangladesh. The West Antarctic ice sheet collapses, pumping 5 metres of water into global sea levels. Southern Europe becomes like the Sahara, with deserts spreading in Spain and Portugal.
+5 °C: The Earth is hotter than at any time for 55 million years. Desert belts expand across Europe, America and Asia. Some populations try to move towards the poles. Most of the world is uninhabitable.
+6 °C: Huge firestorms sweep the planet as methane hydrate fireballs ignite. Seas release poisonous hydrogen sulphide. Most of life on Earth has been extinguished. Humanity’s survival is in question.
how much carbon can we live with?
Climate change will get worse if we allow greenhouse gas emissions to grow unchecked. So where are the emissions coming from? And how much more can the planet take?
scientific predictions
Models show that if we go on with business as usual and fail to address greenhouse gas emissions we can expect average temperatures across the world to rise dangerously. Precisely how much warmer it will get is the subject of huge investigation but the Intergovernmental Panel on Climate Change (IPCC) gives a range of between 2.4°C and 6.4°C above preindustrial levels by the end of this century. If we don’t take action, scientists believe the most likely point within that range will be a rise of 4°C by the end of this century – that’s enough to produce catastrophic results.
measuring carbon
The proportion of carbon dioxide in the atmosphere is usually expressed as parts per million by volume (ppmv); this tells us the concentration of carbon dioxide in numbers of molecules per million molecules of air.
Emissions can also be measured by: the weight of carbon dioxide (carbon plus two oxygen atoms) – in grammes, kilogrammes and tonnes – over a period of time. High levels of emissions are measured in millions of tonnes of carbon dioxide or by the weight of carbon alone. One tonne of carbon is equal to 3.67 tonnes of carbon dioxide.
Other greenhouse gases are sometimes expressed in million tonnes of the carbon dioxide equivalent (Mt CO2e) – in other words, the amount of carbon dioxide that would have the same effect.
how high are global emissions?
In a little more than a century human activity has added 200 billion tonnes of carbon to the atmosphere. Today we are pumping out just over 7 billion tonnes of carbon a year – that’s twenty times the weight of all the water in Lake Windermere. It’s also equivalent to 26 billion tonnes of carbon dioxide. A further 1.6 billion tonnes of carbon dioxide emissions each year come from changes in the way we use land – mostly by cutting down forests that, when growing, play a vital role in soaking up carbon dioxide.
Scientists agree that we need to stabilise emissions, then reduce them. But at what level?
carbon footprint
‘Carbon footprint’ can be useful shorthand to describe the amount of carbon dioxide we generate – individually, in our cities, nationally, or from the products we use. The term ‘footprint’ is also used to describe the impact of emissions, by providing a measure based on the area of things like forests, oceans and grassland that are required to absorb the carbon dioxide.
Later in this chapter, we’ll use this measure of impact to look at the carbon footprints of different countries. Elsewhere in the book we’ll be focusing on carbon dioxide emissions, particularly in the UK, where government figures for emissions are given in weight.
the 2°c target
The UK government, together with the rest of the European Union, has pledged to stabilise greenhouse gases to prevent average global temperatures rising more than 2°C above pre-industrial levels. Allow greater temperature change, climate scientists say, and we start to play havoc with agriculture, the economy and the natural environment – committing millions of people to hardship and millions of species to extinction. Perhaps even more worrying is the prediction that a higher rise than 2°C would increase the risk of spiralling and irreversible climate change.
UK path to a safer future
Steady but steep - the UK needs to make serious cuts in carbon dioxide emissions over the next 40 years to play its part in avoiding runaway climate change. Based on research by the Tyndall Centre for Climate Change Research at the University of Manchester, the chart assumes the need to stabilise atmospheric carbon dioxide at 450 ppm.
To stay within a 2°C rise the science tells us we would need to keep greenhouse gases (and other pollutants) at no more than 450 parts per million carbon dioxide equivalent. But we’re already racing towards that threshold: carbon dioxide alone had already reached 380 ppm in 2006, and emissions are rising by nearly 2 ppm per year.
And there’s more. As a result of the carbon dioxide already in the atmosphere scientists warn that 2°C could be the lowest increase we can hope for.
So how much time do we have to turn things around? Because carbon dioxide stays in the atmosphere for so long, and because it takes a while for it to affect the climate, the fossil fuel we burn in power stations today will still be affecting the climate at the start of the next century. That means we have to reduce emissions as quickly as possible, rather than hoping to make big cuts five years from now. The sooner we make cuts, the better.
Two facts illustrate the urgency of the task that faces us if we want to stay within a 2°C rise:
1 Greenhouse gas emissions have to start falling by 2015. They must then continue to decline.
2 Industrialised countries need to cut emissions by about 90 per cent by the middle of this century.
So can it be done? Some argue that it is unrealistic to expect to cut carbon emissions quickly and deeply enough to stay within 2°C. But the scientific consensus is that we must.
where in the world do the emissions come from?
Most carbon emissions from human activity come from industrialised countries, whose economies rely on manufacturing and transport powered largely by fossil fuels.
The United States, home to fewer than 1 in every 20 people in the world, is responsible for about a fifth of global carbon dioxide emissions.
Europe accounts for 15 per cent of global carbon dioxide emissions, working out at around 9.3 tonnes per person per year. That’s enough to fill two Olympic swimming pools for every person in Europe.
China became the biggest emitter of carbon dioxide in 2006. But China’s emissions per person are less than those of the United States: in 2003 the average American emitted nearly six times as much carbon dioxide as the average person in China.
Across the world average emissions were 3.7 tonnes per person in 2003. But in some African countries, such as Mali and Burundi, they were less than 0.1 tonnes