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Climate change and population

Key points Continuous population growth, fuelled by an expected increase of 2.3 billion people on the planet by 2050, is multiplying the impacts of climate change and will be ecologically unsustainable. In a world of weather extremes, where land is being lost due to rising temperatures, desertification, floods and rising sea levels, the world will not be able to feed, water and sustain even its current 6.8 billion population. As people are forced off their land by climate change, mass migration movements may be joined by up to 200m environmental refugees. The poorest peoples will be most affected. Although northern temperate climates may benefit in the short term, they too will be affected adversely by climate change. Under these circumstances, Europe and the UK will suffer climate change impacts, and will be in no position to sustain larger populations, whether by increasing birth rates or accepting greater migration flows. Stabilisation and decrease of populations, globally and nationally, by encouraging lower fertility and balanced migration, is an essential component of policies to mitigate and adapt to climate change, and urgent action is needed.

CLIMATE CHANGE AND POPULATION SIZE: EARTH

Seven years left?

There's little time left to act, if the latest calculations from the UK's Tyndall Centre for Climate Change Research are right. "If emissions peak in 2015, stabilization at 450ppmv CO2e requires subsequent annual reductions of 4 per cent in CO2e and 6.5 per cent in energy and process emissions." Stabilising CO2e concentration in the atmosphere at 450ppmv gives the world only a slim chance of reducing temperature rise from the pre-industrial age to 2^oC - a target which in itself guarantees little. To be more than 90% sure of not exceeding 2^oC, concentration would need to be stabilised at, or below, 350ppmv CO2e - below the 2008 level.

The recognition of global warming - too little, too late

At the end of 2007, following the United Nations Conference on Climate Change in Bali, there remained little doubt that the world's 6.8 billion people are under serious threat from global warming, and that urgent international action must be taken. There is now both scientific and political consensus that greenhouse gases trapped in the Earth’s atmosphere are due largely to human activities, and that "deep emissions cuts" must take place within as little as a decade to curb warming of our atmosphere, land and sea. If this is not done, further rises in the Earth’s temperature caused by the greenhouse effect may cause dangerous and irreversible climate change.

Global surface temperature averaged 14 degrees Celsius in the 20th century. Although the rise was just 0.6C from 1901 to 2000, the rate of increase tripled in the last quarter of the century and has since accelerated. By the time of the Bali Conference, 2007 looked set to be one of the warmest years on record since 1850, with the 11 warmest years occurring between 1995 and 2006.

What has this to do with population? Put simply, humans are climate changers - directly or indirectly the main cause of climate change. Had efforts been made to stabilise human numbers in 1975, when the planet was inhabited by 4 billion climate changers and modern contraception had arrived, there would be fewer than 6.8 billion climate changers now. Although world population is still growing by some 80 million a year and looks set to grow by another 2.4 billion by 2050, it's not too late to slow it down by peaceful means. According to the UN population projections revised in 2006: "A fertility path half a child below the medium [variant projection, 2006 Revision] would lead to a population of 7.8 billion by mid-century." If the world's mothers reduce the number of children they have accordingly, there could be 1.4 billion fewer climate changers in 2050 - equivalent to the whole population of China. Humans are the solution as well as the problem: human ingenuity is needed to solve the climate change challenge, but it will make the task easier if humans reduce their own increase from 200,000 a day. Think what a difference it would make if all the world's parents decided to "stop at two" children.

DEMOGRAPHIC GROWTH IS A DRIVER OF CLIMATE CHANGE "While the world's climate has always varied naturally, the vast majority of scientists now believe that rising concentrations of greenhouse gases in the earth’s atmosphere, resulting from economic and demographic growth over the last two centuries since the industrial revolution, are overriding this natural variability and leading to potentially irreversible climate change." A guide to the climate change convention process, United Nations Framework Convention on Climate Change, 2002. The UN Framework Convention on Climate Change was adopted by the world's governments on 9 May 2002 and came into force on 21 March 1994.

OPT POPULATION POLICY OPT campaigns for policies to achieve environmentally sustainable population levels both globally and in the UK. The ecological issue is one of population numbers, resource demands and the environmental impacts created by different sizes of population at given levels of affluence and technology. For more details see the Fertility, Migration, Population policy projections, Briefings and submissions and other sections of this website. OPT recommends the following population policies: Globally, that full access to family planning should be provided to all those who do not have it, that couples should be encouraged voluntarily to "Stop at Two" children to lessen the impact of family size on the environment, and that this should be part of a holistic approach involving better education and equal rights for women. In the UK, that population should be allowed to stabilise and decrease by not less than 0.25% a year to an environmentally sustainable level, by bringing immigration into numerical balance with emigration, by making greater efforts to reduce teenage pregnancies, and by encouraging couples voluntarily to "Stop at Two" children.

What greenhouse gases do to the human habitat

The main offender in volume terms is carbon dioxide (CO2), which is released mainly by burning fossil fuels such as coal, oil and natural gas. CO2 from fossil fuels accounts for 59% of the potential global warming effect of man-made greenhouse gas emissions, and CO2 released by changes in land use, together with other greenhouse gas releases, contributes about 40%. With an atmospheric lifetime of between 5 and 200 years, CO2 concentrations will rise for a long time after annual emissions levels are stabilised and reduced. Its climate change effects include droughts and storms on land, and melting icecaps, rising temperatures and acidity in the oceans. The effects on food supply are already apparent, with desertification, floods and other extreme weather events causing land to be taken out of agricultural production: food and commodity prices have risen steeply as vast populations create rising demand that can no longer easily be met.

The concentration of carbon dioxide in the atmosphere has risen by about a third since 1850 and is higher than it has been for 650,000 years. In the pre-industrial centuries up to 1750, carbon dioxide concentrations remained fairly stable at 280ppm (parts per million). Each year since global measurements of CO2 began, the amount of carbon dioxide in the atmosphere has increased. Emissions concentrations grew by some 80% between 1970 and 2004, reaching 379ppm in 2005, and by 2008 were growing by 0.5% a year - a rate that would result in concentrations doubling in 140 years. In 1990, according to the US Energy Information Administration, the world pumped 21.2 billion metric tonnes of CO2 into the atmosphere, rising to 26.9 billion MT in 2004. Total man-made carbon dioxide emissions in 2004, according to the IPCC, were 38 billion MT - an average 6 tonnes every each human being on earth. With another 2.4 billion people expected in 2050, emitting at that rate, emissions would be some 15 billion tonnes higher.

"Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of 0.1C per decade would be expected", warned the Fourth Assessment Report (FAR) published by the Intergovernmental Panel on Climate Change (IPCC) in 2007. In 2001 the IPCC had forecast that average global surface temperature would rise by 1.4C-5.8C in the 21st century, but estimates that this threshold would not be breached until the end of the century have been superseded by recent climate data showing more rapid emissions accumulation and climate effects than previously assumed. To prevent a temperature rise of 2.0-2.4C from pre-industrial levels, with CO2 concentrations stabilising at 350-400ppm, would need cuts of 50-85% in greenhouse gas emissions by 2050, according to the IPCC Fourth Assessment Report. Most scientists agree that a sustainable climate change target means limiting global temperature increase in the 21st century to no more than 2C above pre-industrial levels, a limit that has already been adopted by the European Union. In March 2007 EU leaders agreed an ambitious target 20% reduction in greenhouse gas emissions by 2020.

The latest IPCC figures indicate that "60-80% of the reductions would come from energy supply and use, and industrial processes, with energy efficiency playing a key role in many scenarios". In 2001 the UNFCCC Climate Change Information Kit stated that "Future greenhouse gas emissions will depend on global population, economic, technological and social trends. The link to population is clearest: the more people there are, the higher emissions are likely to be." Yet environmentally sustainable population policies were still not on the agenda at Bali in 2007.

Are the climate scientists wrong? The first quantitative link between atmospheric carbon dioxide concentrations and climate change was made in 1896 by Swedish scientist Svante Arrhenius, who predicted a temperature rise of 5-6 degrees Celsius for a doubling of CO2. By the 1980s the connection was clear and supported by scientific evidence. But it took another 25 years for the evidence to be widely accepted. There is always room for doubt. However, in spite of large amounts of funding for research into climate change over the last decade, no alternative theory, including the contribution to warming of solar flare activity, has stood up to close scrutiny. And in the increasingly unlikely event that the world's climate scientists are proved wrong, the case for reducing human population to a sustainable level still stands - on the basis of the many other forms of environmental damage being caused by humans to their environment, and because of the speed at which they are depleting non-renewable resources.

Atmospheric carbon is increasing by about 3.5 billion tonnes a year, and the IPCC has projected that if their atmospheric concentration, which reached 379ppm in 2005, is not checked, it could reach 650-970 parts per million at stabilisation. Until recently most climate scientists agreed that it would be dangerous for CO2 concentration to exceed 550ppm. But the threshold that would trigger a 2C temperature rise and lead to irreversible global warming is now believed to be as low as 400ppm of CO2-equivalent concentrations. The 1997 Kyoto Protocol asked industrialised countries to reduce greenhouse gas emissions by as little as 5% from 1990 levels by 2012, far below the cuts required now.

Graphic scenarios of temperature rise and shrinking sea ice coverage if concentrations of CO2 more than double over the 21st century have been produced by the Met Office Hadley Centre in the UK, following a 2005 scenario suggesting rises of up to 11C. Studies by Southampton and Plymouth universities the following year indicated that heat stores in oceans could raise global atmospheric temperature by almost 9C. Demonstrating the feedback warming this would trigger, analysis by the Centre for Global Atmospheric Monitoring in Reading concluded in April 2004 that a rise of 2.7C in global temperatures might be enough to cause irreversible melting of the 2km-thick Greenland ice sheet, leading to a global sea level rise of 7 metres during the next 1,000 years. Recent findings show that melting is accelerating at lower levels of temperature increase than the maximum forecast: in 2003 Greenland experienced the second-highest meltwater run-off from its ice sheet in 50 years, followed by a record-high melt in summer 2005. And a Sheffield University study indicates that the 2005 record was broken again in 2007.

World population limit 2.1 billion The global population level needed in order to stabilise carbon dioxide may be as low as 2.1 billion, if other carbon dioxide-reducing measures are excluded. This allows for a relatively low per capita energy consumption of 2kW (17,250 kWh per annum) (US citizens currently about use about 9kW). Andrew Ferguson, OPT. For more information see Perceiving the Population Bomb , World Watch, Jul/Aug 2001.

For countries that already have hot and dry climates, a rise of far less than 5.8 ^o implies increasing droughts that could turn whole countries into desert, with consequent famine and migration pressures. Africa, for example, is expected to bear the brunt of global warming: if current trends continue temperatures in sub-Saharan Africa could rise by 2C with rainfall declining by 10% [Avoiding Dangerous Climate Change, A Symposium on Stabilisation of Greenhouse Gases, Exeter, UK, February 2005].

Such a collapse is now believed to have led to the extinction of almost all animal and plant species in earlier times. A global temperature rise higher than 6C is expected to be self-feeding. In scientific terms, it would result in 'positive feedback loops' which amplify the effects of climate change: the die-back of the Amazon rainforest as the climate warms would release yet more carbon dioxide into the atmosphere. This is already happening. A 3C warming would release up to 85 per cent of the 5,000 billion tonnes of methane which is locked away in deep ocean sediments and in the permafrost on the land, after a few thousand years [Professor David Archer, Dept of Geophysical Sciences, University of Chicago]. As a potent greenhouse gas, this additional release of methane would raise the temperature still further and ultimately destroy all human life.

The World Health Organisation estimated that climate change was responsible for approximately 2.4 % of worldwide diarrhoea and 6% of malaria in some middle-income countries in the year 2000, and contributed to a total of 150,000 deaths worldwide (killing an estimated 35,000 people in Europe during the 2003 heatwave). It also contributes to the deaths of some 70 million a year from famine. Loss of healthy life years in low income African countries, according to a study by Professor A. J. McMichael of Australian National University, is predicted to be 500 times that in Europe, and in sub-Saharan Africa 20-70 million people could be added to more than 110 million people already living in regions prone to malaria epidemics.

While technology and energy conservation can alleviate greenhouse gas emissions, growing populations as well as growing affluence are likely to negate these improvements. Some countries (for example, China) have population stabilisation policies, but few have explicit targets to reduce population numbers. In spite of having a population policy, India's population of 1.1 billion is set to overtake China's 1.4 billion, and the growing impact of these vast numbers of emitters as their energy consumption rises has only recently been acknowledged.

At the end of 2007 the International Energy Agency (IEA) reported that CO2 emissions were some 20% higher than in 1997, the year of the Kyoto Protocol agreement. "Absent new policies, energy-related carbon emissions will increase by almost 60%, reaching 42 billion tonnes (Gt) in 2030", forecast the IEA. This was 1.5Gt higher than its 2006 forecast, due to much greater coal use than expected, driven by high oil and gas prices. Alongside energy conservation and carbon-free energy substitution and strategies, population policies can make a contribution to reducing fossil fuel demand, by reducing the expected numbers of extra fossil fuel burners.

In 1992 the IPCC suggested that in order to stabilise carbon dioxide concentrations in the atmosphere at the 1990 level of 353 parts per million, emissions needed to be cut by at least 60% from their 1990 level of 21.8 billion tonnes to 9 billion tonnes a year (carbon is usually expressed as CO2 divided by 3.664). "Stabilising [CO2] concentrations at, for example, 450 ppm would require worldwide emissions to fall below 1990 levels within the next few decades," indicated the UNFCC in 2001. Earlier projections have been proved over-optimistic, and time will soon be up.

Both emissions and population levels need to be reduced

In OPT's view, necessary emissions reductions cannot be achieved without parallel population stabilisation programmes. With a 2009 world population of 6.8 billion, projected to rise to 9.1 billion in 2050, a worldwide desire to raise living standards may be impossible to achieve without catastrophic global warming. The UK, for example, was one of the world's better performers in emissions reduction in the 1990s, but by 2007 it had managed to reduce CO2 emissions by only 5.5% from 1990 levels. Measures to reduce emissions are under way (for example the EU emissions trading scheme), but are unlikely to be effective on their own. Emissions reduction framework strategies need to be global, fair, and display no 'perverse incentives' that encourage population or consumption growth: strategies based on reducing per capita consumption alone would be negated by perpetual population increase.

In the absence of population policies, population levels are likely to be so high by the time emissions 'convergence' is achieved that climate change will already have caused lasting damage to Earth. OPT has calculated, on the basis of necessary carbon dioxide emissions limits alone, shared between individual countries at their 1990 population levels, as well as ecological footprinting calculations, that Earth cannot support more than 2.77 billion people at current levels of technology and consumption. See Sustainable numbers . Put simply, the IPCC limit for a stable atmosphere is about 9 billion tonnes of carbon emissions a year, giving a sustainable level of only 1.4 tonnes per capita for today's 6.8 billion people. This target will be impossible to meet without incorporating sustainable (lower) population levels. See Crucial limits. Improvements in technology and other factors will raise maximum sustainable populations from the levels suggested in this table, but perhaps not by much. At the post fossil-fuel stage, maximum sustainable population size is likely to be restricted by the land demands and low energy yields of green energy rather than by greenhouse gas emissions limits.

Climate change prospects for the UK

The climate change scenario for the UK is one of initial warming. Longer, hotter, drier summers and milder but wetter winters have already arrived and the trend will continue, with a temperature rise of between 0.5 and 1C forecast for 2040 and 1-5C by 2100. But a higher rise is possible, with some climate scientists suggesting even faster warming. In the UK, 2006 was the warmest year since records began in 1659. In June 2003 the Foresight Flood and Coastal Defence Project run by the Office of Science and Technology predicted that large areas of the UK could be at risk of repeated severe floods and wave surges by 2080: in its worst-case scenario flood damage alone was expected to cost £20 billion.

Much depends on the rate at which glaciers and ice sheets melt. During the 20th century, global sea level rose by around 20 cm, a rate that may be higher than at any time during the past thousand years. If greenhouse gas emissions are not reduced, the UK Meteorological Office estimates that sea levels may rise a further 41cm by 2080, mainly through the melting of small glaciers and ice sheets and the thermal expansion of sea-water with rising temperatures. But this estimate takes no account of the potentially catastrophic melting of major ice sheets, such as the Greenland and West Antarctic ice sheets, which could eventually raise sea levels by several metres. The Benfield Hazard Research Centre at University College, London, has produced maps of Britain showing the additional impact of sea-level rise under three scenarios: the melting of either the Greenland or West Antarctic ice sheets (7m), the melting of both (13m) and the additional melting of the gigantic East Antarctic ice sheet (84m). A 7m rise would inundate many of the UK's coastal towns and cities while the loss of the East Antarctic sheet would drown much of eastern and southern England and separate Scotland from England and Wales. The latter scenario is regarded as only possible many thousands of years into the future, the result of a runaway greenhouse effect, but the West Antarctic ice sheet appears to be increasingly unstable and may have a 1 in 20 chance of collapsing and melting within the next 200 years.

CLIMATE CHANGE AND POPULATION SIZE: UK

UK Climate change policy

A rise of up to 5C in temperature implies a Mediterranean climate in the UK in the short term that will become dangerously volatile in the long term. Earlier research indicating a 'big freeze' a century or more ahead, as the effect of freshwater entering the oceans from melting glaciers irreversibly disrupts ocean currents, including the Gulf Stream that warms the UK, and reduces UK temperatures to those of Newfoundland, Siberia or worse, has recently been qualified. Climate modelling carried out in 2005-6 suggests that a failing Gulf Stream might act only as a brake on warming, and that UK temperatures will continue to rise.

Former Prime Minister Tony Blair pledged to take a lead on climate change policy before the UK became leader of the G8 group of industrialised countries in January 2005 and the European Union in July 2005, and as part of this effort an international scientific conference took place in the UK in February 2005 to try to establish an upper limit for global temperature rise before the consequences become 'catastrophic'. This was a welcome political initiative - but at both the global and UK level measures to reduce greenhouse gas emissions will be constantly undermined if UK population - the number of climate changers and energy consumers - continues to grow.

The UK contributes about 2% of global man-made CO2 emissions, but every nation's contribution counts. In its Energy White Paper of 2003, the government made a commitment to increase renewable energy, pledging to cut carbon emissions by 20% (below 1990 levels) by 2010 and 60% by 2050. But decisions on building new nuclear power stations were postponed and the target for 20% of UK electricity to be met from renewable sources (wind, tidal, wave, solar, biomass etc.) by 2020 was downgraded to an 'ambition' - indicating just how difficult it would be to meet.

Following the May 2005 General Election, there has been increasing focus on the UK's widening energy deficit, and the consultation process for a new energy policy began in 2006. In January 2008, new prime minister Gordon Brown took a decision to build up to 10 new nuclear power plants by 2020, which is expected to reduce total UK carbon emissions by some 5%. And in January 2008 the EU 27 produced its controversial renewable energy strategy "every nation in the 27-member bloc is required to increase its share of renewables by 5.5% from 2005 levels". The UK will have to increase its renewables contribution to total energy supply from 1.3% in 2005 to 15% by 2020 in just 12 years - needing large areas of land for building wind farms and growing renewable energy crops. In an already densely populated country, where every additional UK citizen is likely to generate over 750 tonnes of carbon dioxide over a lifetime, land is already scarce.

The 'Kyoto basket' of six greenhouse gases fell by 15.3% between 1990 and 2006 - more than the 12.5% cut required by the Protocal target. In 1990 the UK's CO2 emissions were 590 million tonnes, but after initial reductions, largely due to a switch from coal and oil to gas, they climbed back to 543.7 Mt in 2006 , giving a reduction of only 7.8%. Forty percent of CO2 emissions were from the energy supply sector, 22% from road transport, 17% from business and 15% from residential fossil fuel use. Carbon dioxide accounted for about 85% of the UK's man-made greenhouse gas emissions in 2006, and with 557 million tonnes emitted, each UK inhabitant produced just over 9 tonnes on average a year. So annual population growth of 350,000 - all other things being equal - adds another 3.2 million tonnes of emissions to the total, and every addition to UK population means more severe cuts to achieve existing targets.

UK Population change and greenhouse gas emissions

The government has still not acknowledged that its pro-population growth policies have undermined its climate change policies. By adding over two million more people (extra producers of greenhouse gas emissions through household, transport and business use) to the population of the UK since 1997, and by allowing the number of climate changers to rise by some 350,000 people a year from 2004-2007, the government's population policy has undermined most of its environmental goals. In 2004, households accounted for 24% of CO2 emissions, road transport for 33%, and non-energy industries for 27%. With more than five new cities the size of London needing to be built to accommodate projected population growth to 85 million by 2081, emissions cannot easily be curbed.

Although the UK looks set to achieve its Kyoto greenhouse gas emissions target, it is unlikely to meet its internal 20% CO2 emissions target by 2010. Achieving this and a 60% reduction in CO2 emissions by 2050 would be helped by the population policy that OPT recommends. The first chart below shows the simple effect of continued UK population growth at the 2004 rate of 0.4% per annum on CO2 emissions, on an assumption that emissions can be reduced at 1% a year by other measures. The second chart shows the effect of changing the government's implicit population growth policy to one of gradual decrease of 0.25% a year. The difference in CO2 emissions, all other factors being equal, is 29 million tonnes of emissions in 2050. Since 2004, the annual population growth rate has risen to 0.6% a year and is projected to increase at about that rate until 2050.

Is it wise to allow further UK population growth?

No. Warming during the 21st century is already causing changes in the timing of seasons and extreme weather events, which are affecting agricultural yields and causing damage to the country's infrastructure. UK per capita CO2 emissions of over nine tonnes a year for a population of 60 million already exceed the world average of about four tonnes a year and a sustainable worldwide limit of 1.44 tonnes per capita at current population levels. With its population growing by nearly a million every three years, the situation can only get worse: every additional UK citizen is likely to generate over 750 tonnes of carbon dioxide over a lifetime.

To meet IPCC emissions targets on a basis that allows all countries a ’modest European standard of living’, OPT maintains that, in addition to emissions reduction policies, populations must be allowed to reduce gradually to a long-term sustainable level. UK population is currently growing at 0.6%-0.7% a year. OPT believes an environmentally sustainable population for the UK may be lower than 30 million in the 22nd century, and recommends a gradual decrease of not less than 0.25% a year. At this minimum rate UK population would not halve until 2282, however, so the rate of decrease may need to be raised.

The October 2002 issue of the OPT Journal highlighted the temporary nature of carbon sequestration as a solution to global warming, reinforcing the view that Earth’s population is overshooting its sustainable carbon emissions level.

More information on climate change

Websites with information on climate change. While all these organisations recognise that climate change is currently driven by the activities of [6.8 billion] humans, none yet acknowledges that reversing population growth needs to be part of a solution:

OPT maintains that it is too late for greenhouse gas emissions to be reduced to sustainable levels by energy conservation, technological innovation, emissions trading and economic incentives alone. Low birth rates should also be strongly encouraged so that world population - instead of rising to 9.1 billion in 2050 - stabilises and reduces gradually from its current 6.8 billion to less than 3 billion over a longer period, allowing genuinely sustainable development to take place.