[1]  i.e. to the Vienna Convention for the Protection of the Ozone Layer

[2]  http://www.interacademies.net/10878/13951.aspx

[3]  See AR5, SPM, 1.1

[4]  ibid. 1.2

[5]  ibid.

[6]  C. Pelejero et al, 2010, ‘Paleo-perspectives on ocean acidification’, Trends in Ecology and Evolution, 25,6, 332-4

[7]  Such carbonates were conclusively identified by the Mars Spirit Rover. See R Morris et al., 2010: ‘Identification of            

      Carbonate-Rich Outcrops on Mars by the Spirit Rover’, Science, 23 July 2010, vol 329, no 5990, pp. 421-4

[8]  AR5, SPM1.2

      Climate change in the Fertile Crescent and implications of the recent Syrian drought, PNAS vol.112, no. 11, Colin P. Kelley       et al.,  3241–3246, doi:10.1073/pnas.1421533112

[10]  http://www.defense.gov/pubs/150724-Congressional-Report-on-National-Implications-of-Climate-Change.pdf

[11]  http://earthobservatory.nasa.gov/Features/Coral/

[12]  http://www.oecd.org/env/indicators-modelling-outlooks/oecdenvironmentaloutlookto2050theconsequencesofinaction-keyfactsandfigures.htm

[13]  AR, SPM, 3.4

[14]  AR4. 10.4.2

[15]  AR5, SPM 2.3

[16]  See at http://www.wwf.se/source.php/1169157/Stern%20Report_Exec%20Summary.pdf

[17]  See AR5, SR, 3.4

[18]  AR5, SR, Box 3.1

[19]  Wagner and Weitzman, Climate Shock – The Economic Consequences of a Hotter Planet, Ch 1, p. 23. For uncertainties             
regarding the social costs of carbon see AR5, WG3, 3.9.4, http://www.ipcc.ch/pdf/assessment-    


[20]  http://www.imf.org/external/pubs/ft/wp/2015/wp15105.pdf

[21]  Royal Society, Geoengineering the Climate: Science, governance and uncertainty, London, 2009, p.1

[22]  AR5, SPM 3.4Type your paragraph here.

What impacts have there been to date? | Back to top
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‘Mitigation’ (reducing the problem) refers to actions to prevent or limit climate change (eg by controlling emissions or preserving and developing carbon sinks). Adaptation (adapting to the consequences) is aimed at attempting to make nature, society and the economy less vulnerable to a changing climate (eg the construction of flood defences or the relocation of populations).

There can be no general formula for dividing resource between the two. For some countries (such as low lying island states) adaptation may be an immediate priority. More generally, however, effective adaptation plans depend on accurate projections for warming and its consequences. A credible mitigation strategy, focussed on keeping temperature rises below an agreed limit, provides the basis for adaptation planning: the greater the success of mitigation efforts, the less the requirement for adaptation.

​​​In economics an externality is a cost or benefit that affects a party that has not chosen to incur that cost or benefit. Unregulated markets with significant externalities lead to prices that do not reflect the full social cost or benefit of their transactions and are therefore inefficient.

It has been estimated that for each of the 35 billion tonnes of CO2 currently being emitted annually is causing $40 worth of damage to the planet, possibly much more[19]. The market might be corrected by ensuring such costs were reflected in the price of fossil fuels.

Unfortunately the opposite is happening: the IMF has recently calculated that global fossil fuel subsidies amount to $5.3 trillion a year (or $10 million a minute)[20].

With appropriate incentives and disincentives the market would instead be working to support the transition.

With five degrees of global warming, an entirely new planet would come into being – one largely unrecognizable from the Earth we know today. The remaining ice sheets would eventually be eliminated from both poles. Rainforests have already burned up and disappeared. Rising sea levels have inundated coastal cities and are beginning to penetrate far inland into continental interiors. Humans will be herded into shrinking zones of habitability by the twin crises of drought and flood.

To find out what the planet would look like with five degrees of warming, one must largely abandon the models and venture far back into geological time, to the beginning of a period known as the Eocene. Fossils of sub-tropical species such as crocodiles and turtles have all been found in the Canadian high Arctic dating from the early Eocene, 55 million years ago, when the Earth experienced a sudden and dramatic global warming. These fossils even show that breadfruit trees were growing on the coast of Greenland, while the Arctic Ocean saw water temperatures of 20C within 200km of the North Pole itself. There was no ice at either pole; forests were probably growing in central Antarctica.

The IPCC projections are expressed in less graphic but consistent terms:

‘Climate change will amplify existing risks and create new risks for natural and human systems. Risks are unevenly distributed and are generally greater for disadvantaged people and communities in countries at all levels of development.’[2.3]

‘Climate change is projected to undermine food security. Due to projected climate change by the mid-21st century and beyond, global marine species redistribution and marine biodiversity reduction in sensitive regions will challenge the sustained provision of fisheries productivity and other ecosystem services (high confidence).’[2.3.1, 2.3.2]

‘Climate change is projected to reduce renewable surface water and groundwater resources in most dry subtropical regions (robust evidence, high agreement), intensifying competition for water among sectors (limited evidence, medium agreement).’[2.3.1, 2.3.2]

‘Until mid-century, projected climate change will impact human health mainly by exacerbating health problems that already exist (very high confidence). Throughout the 21st century, climate change is expected to lead to increases in ill-health in many regions and especially in developing countries with low income, as compared to a baseline without climate change (high confidence).’[2.3.2]

‘In urban areas climate change is projected to increase risks for people, assets, economies and ecosystems, including risks from heat stress, storms and extreme precipitation, inland and coastal flooding, landslides, air pollution, drought, water scar- city, sea level rise and storm surges (very high confidence). These risks are amplified for those lacking essential infrastructure and services or living in exposed areas.’[2.3.2]

‘Aggregate economic losses accelerate with increasing temperature (limited evidence, high agreement).’[2.3.2]

‘Climate change is projected to increase displacement of people (medium evidence, high agreement). Populations that lack the resources for planned migration experience higher exposure to extreme weather events, particularly in developing countries with low income. Climate change can indirectly increase risks of violent conflicts by amplifying well-documented drivers of these conflicts such as poverty and economic shocks (medium confidence).’[2.3.2]

‘Without additional mitigation efforts beyond those in place today, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, widespread and irreversible impacts globally (high confidence). In most scenarios without additional mitigation efforts ... warming is more likely than not to exceed 4 degrees C above pre-industrial levels by 2100.’[2.3]

Ocean acidification

Marine organisms will face progressively lower oxygen levels and high rates and magnitudes of ocean acidification, with associated risks exacerbated by rising ocean temperature extremes. Coral reefs and polar systems are particularly vulnerable[15].

​When the Earth was last 4 degrees warmer, approximately 25 million years ago, there was no ice at either pole. Global warming of this magnitude would eventually leave the whole planet without ice for the first time in 40 million years, leading to sea rises of 50 to 70 meters.

Collapse would not happen instantaneously – it would take centuries, probably millennia, to melt all of the Antarctica’s ice. But the destabilization of both Antarctic ice sheets could yield sea-level rises of a meter or so every 20 years – far outside the adaptation capacity for many countries and peoples (resulting in large-scale migrations and international conflict).

Australia – except perhaps the extreme north and Tasmania – will be unable to support significant crop production because of heat-waves and declining rainfall.

In India, with land temperatures soaring to 5 degrees or more above current levels, it will be too hot for most crops to survive. In western areas of the subcontinent, already arid areas get drier still, compounding the water emergency arising from the de-glaciation of the Himalaya and Karakoram mountain chains, forcing a human migration of hundreds of millions in search of food and water.

The world’s weather will grow increasingly haywire.

Ocean acidification is a phenomenon distinct from global warming, sometimes referred to as ‘the other carbon dioxide problem’, or, more colorfully, as ‘global warming’s evil twin’. The ocean currently absorbs about half of the CO2 emissions from burning fossil fuels, limiting the impact on global warming, but increasing ocean acidity. Seawater is depleted of the carbonate minerals that many sea creatures, from corals to plankton, use to build their shells or skeletons. This undermines the base of the ocean food chain, threatening the health and prosperity of all those who depend on the sea for sustenance and income.

IAP, the global network of science academies, issued a statement on ocean acidification in 2009, with the following headline messages:

At current emission rates models suggest that all coral reefs and polar ecosystems will be severely affected by 2050 or potentially even earlier;
Marine food supplies are likely to be reduced with significant implications for food production and security in regions dependent on fish protein, and human health and wellbeing;
Ocean acidification is irreversible on timescales of at least tens of thousands of years;
Even with stabilisation of atmospheric CO2 at 450 ppm, ocean acidification will have profound impacts on many marine systems. Large and rapid reductions of global CO2 emissions are needed globally by at least 50% by 2050.

Although different problems, global warming and ocean acidification have a common cause: anthropogenic CO2 emissions.

Geo-engineering has been defined as ‘the deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change’[21]. If the idea is not immediately attractive, the prospect of increasing climate change demands serious consideration of all conceivable mitigations.

A leading proposal is to inject sulphur dioxide into the stratosphere where it could reflect the sun’s radiation, without causing air pollution.

There are, unsurprisingly, a number of concerns about such approaches. AR5 concludes:

Solar radiation management (SRM) involves large-scale methods that seek to reduce the amount of absorbed solar energy in the climate system. SRM is untested and is not included in any of the mitigation scenarios. If it were deployed, SRM would entail numerous uncertainties, side effects, risks and shortcomings and has particular governance and ethical implications. SRM would not reduce ocean acidification. If it were terminated there is high confidence that surface temperatures would rise very rapidly impacting ecosystems susceptible to rapid rates of change.[22]

More specifically scientific modelling suggesting sulphur dioxide injections would disrupt the Asian and African monsoons.

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Two degrees may not sound like much, but it is enough to make most European summers as hot as 2003, when 30,000 people died from heatstroke. Extreme summers will be hotter still. Water shortages will be aggravated as the southern Mediterranean loses a fifth of its rainfall.

Two degrees is also enough to cause the collapse of the Greenland ice sheet, which would eventually raise global sea levels by seven meters (much of the ice-cap disappeared 125,000 years ago, when global temperatures were 1-2 C higher than now).

This melting will also continue to affect the world's mountain ranges. In Peru all the glaciers will disappear from the Andean peaks that currently supply Lima with water. In California, the loss of snowpack from the Sierra Nevada - three-quarters of which could disappear in the two-degree world - will leave cities such as Los Angeles increasingly thirsty during the summer. Global food supplies, especially in the tropics, will also be affected but while two degrees of warming will be survivable for most humans, a third of all species alive today may be driven to extinction as climate change wipes out their habitat.

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Climate change

Greenhouse gases (GHGs) in the atmosphere absorb and retain energy from the sun. As their presence increases so the planet warms up (and vice versa).  GHGs have determined the fate of the other rocky planets in the solar system. Venus is too hot for life, having suffered a runaway greenhouse effect: its oceans boiled away and most of its carbon ended up in the planet’s atmosphere as a blanket of carbon dioxide. Its mean surface temperature is now 462 degrees Celsius. The reverse happened on Mars, which began life warm and wet with abundant water before its carbon dioxide became trapped in carbonate rocks[7]. Its mean surface temperature is now -63 degrees Celsius.

AR5 attributes the rise in concentrations of GHGs to ‘anthropogenic … emissions since the pre-industrial era.’[8]

Ocean acidification

When CO2 is absorbed in water, carbonic acid is formed, which then dissociates into hydrogen ions, increasing ocean acidity.

​Climate change

Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen. Each of the last three decades has been successively warmer than any preceding decade since 1850. Over the period 1880 to 2012, the planet, as a whole, has warmed by 0.85 degrees Celsius[3].

Currently GHG concentrations in the earth’s atmosphere are higher than at any point in at least the last 800,000 years[4]; and rising fast.

Ocean acidification

The pH of ocean surface water has decreased by 0.1, corresponding to a 26% increase in acidity[5]. This is probably more acidic than at any point in the last 20 million years[6].

​​Climate change

The UN projects that global population will reach 9.2 billion by 2050; while the OECD predicts that the global GDP will quadruple by the same date[12]. Population and economic growth mean increasing energy consumption and will, without corrective action, drive levels of emissions ever higher.

AR5 concludes that, without additional efforts to reduce GHG emissions beyond those in place today, by 2100 the average global temperature will have increased by 3.7 to 4.8 degrees Celsius compared to the period 1850-1900. When natural climate uncertainty is factored in the range expands to 2.5 to 7.8 degrees Celsius[13]. The actual emissions scenario that will be realised is, of course, a product of our own decisions.

Ocean acidification

Ocean acidification is projected to rise by 100-150% by 2100[14].

What is the connection between climate change and ocean acidification? | Back to top

3 degrees Celsius may be the "tipping point" where global warming veers out of control, leaving us powerless to intervene as planetary temperatures soar. Computer model projections show worsening droughts making Amazonian trees, which have no evolved resistance to fire, much more susceptible to burning. Once this drying trend passes a critical threshold, any spark could light a firestorm. And once the trees have gone, desert will take its place. The carbon released by the forests' burning will be supplemented by more from the world's soils. This could boost global temperatures by a further 1.5ºC - tipping us straight into the four-degree world.

Three degrees alone would see increasing areas of the planet being rendered uninhabitable by drought and heat. In southern Africa, a huge expanse centered on Botswana could see a remobilization of old sand dunes, much as is projected to happen earlier in the US west. This would wipe out agriculture and drive tens of millions of climate refugees out of the area. The same situation could also occur in Australia, where most of the continent will fall outside the belts of regular rainfall.

In northern Europe and the UK, summer drought will alternate with extreme winter flooding as torrential rainstorms sweep in from the Atlantic - perhaps bringing storm surge flooding to vulnerable low-lying coastlines as sea levels continue to rise. Those areas still able to grow crops and feed themselves may find they are besieged by millions of climate refugees from the south.

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Will tackling emissions undermine economic growth? | Back to top

Climate change

AR5 SR 1.3.2 and 1.4 provides a summary of current impacts. Below are some excerpts:

In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans.

In many regions changing precipitation or melting snow and ice are altering hydrological systems, affecting water resources in terms of quantity and quality (medium confidence).

Glaciers continue to shrink almost worldwide due to climate change (high confidence), affecting runoff and water resources downstream (medium confidence).

Increases in the frequency or intensity of ecosystem disturbances such as droughts, windstorms, fires and pest outbreaks have been detected in many parts of the world and in some cases are attributed to climate change (medium confidence).

Oxygen minimum zones are progressively expanding in the tropical Pacific, Atlantic and Indian Oceans, due to reduced ventilation and O2 solubility in warmer, more stratified oceans and are constraining fish habitat (medium confidence).

Since AR4, several periods of rapid food and cereal price increases following climate extremes in key producing regions indicate a sensitivity of current markets to climate extremes among other factors (medium confidence).

It is likely that the frequency of heat waves has increased in large parts of Europe, Asia and Australia. It is very likely that human influence has contributed to the observed global scale changes in the frequency and intensity of daily temperature extremes since the mid-20th century. It is likely that human influence has more than doubled the probability of occurrence of heat waves in some locations.

It is likely that extreme sea levels (for example, as experienced in storm surges) have increased since 1970, being mainly the result of mean sea level rise.

Impacts from recent climate-related extremes, such as heat waves, droughts, floods, cyclones and wildfires, reveal significant vulnerability and exposure of some ecosystems and many human systems to current climate variability (very high confidence). Impacts of such climate-related extremes include alteration of ecosystems, disruption of food production and water supply, damage to infrastructure and settlements, human morbidity and mortality and consequences for mental health and human wellbeing. For countries at all levels of development, these impacts are consistent with a significant lack of preparedness for current climate variability in some sectors.

Recent research offers more specific examples. On May 9, 2015, The Economist reported on work at Oxford University demonstrating the relationship between climate change and particular extreme weather events. One example given is the Australian heat wave of 2013 (‘the angry summer’), described as ‘virtually impossible’ without climate change. The article concludes:

Worryingly, the risk of an extreme event seems to rise exponentially as mean temperatures creep up. The probability of a heat extreme is twice as great at 2°C of warming than at 1.5°C.

Research from Columbia University illustrates how climate change acts as a ‘threat multiplier’, for example in relation to matters of national and international security. Drying and drought in Syria from 2006 to 2011—the worst on record — had a devastating impact on agriculture, causing many farming families to migrate to the cities. This influx, the researchers conclude, added to existing social stresses (including refugees from Iraq), which erupted into civil war[9].

The international security consequences of climate change have recently been considered in a report of the US Department of Defence[10]:

The National Security Strategy, issued in February 2015, is clear that climate change is an urgent and growing threat to our national security, contributing to increased natural disasters, refugee flows, and conflicts over basic resources such as food and water.1 These impacts are already occurring, and the scope, scale, and intensity of these impacts are projected to increase over time.

Ocean acidification

The interaction of different stressors (such as global warming, ocean acidification and reduced levels of oxygen) makes it difficult to attribute specific observed consequences to ocean acidification. However, coral reefs, probably the world’s most important oceanic habitat, are already in decline almost everywhere, with as much as 27% having already been lost[11].

Climate change

It’s impossible to say with certainty - we have no experience of such temperatures. A planet 4 degrees warmer would be hotter than at any time since the Miocene era some 25 million years ago (modern humans have only been around for about 200,000 years). Towards the upper end of the range the implications are surely dire.

Paleoclimatology and scientific modelling provide the basis for more detailed projections.  Mark Lynas, a journalist and Research Associate at Oxford University’s Centre for the Environment, summarised the scientific research in his book, ‘Six Degrees: Our Future on a Hotter Planet’. The following projections derive from his work.

Inevitably experts approach climate change from a variety of political perspectives and differ in certain respects. There is ongoing debate, for example, about the level of 'climate sensitivity'  (i.e. the climactic response to doubling the level of CO2 concentration in the atmosphere).  As evidenced by the reports of the IPCC, however, in relation to the following key conclusions there exists a broad scientific consensus:

Global warming greater than 1.5 or 2 degrees Celsius risks irreversible damage to human and natural systems;
We are currently at high risk of warming in the region of 4 degrees Celsius before the end of the century;
Averting potentially catastrophic climate change requires urgent, coordinated political action.

There are two main factors contributing to the illusion of doubt.

First, discussion of climate change has been politicized. Some argue it demonstrates fundamental failings in the political system, a view, which provokes a mainstream political and media backlash. Climate change becomes associated with a contentious combination of ‘green’ positions (such as challenge to the goal of economic growth and opposition to nuclear energy and genetically modified food). Public opinion is divided, eroding the mandate for political action.

Second, there are vested interests which 'make doubt their business'. It is notable, however, that even oil and gas majors are now calling for governments to take strong action at COP21 including by introducing carbon pricing (see http://www.bp.com/en/global/corporate/press/press-releases/oil-and-gas-majors-call-for-carbon-pricing.html).

The consequences of GHG emissions (both global warming and the acidification of the ocean) present challenges which are fundamentally technical in nature, similar in kind to the threat to the ozone layer from chlorofluorocarbons (CFCs). The 1987 Montreal Protocol[1], succeeded in phasing out CFC production, averting fatal damage to the ozone layer. The threats from GHGs are capable of being addressed through a similar process. Climate change, as an issue, must be separated from broader, more intractable political debates. All those who recognize the need for urgent, coordinated political action should strike for the center ground.

Our economies remain heavily dependent on fossil fuels. Drastic emission cuts, like any process of significant change, is likely to be painful in a variety of ways. This has led some to view economic growth and climate change as conflicting policy drivers. In fact the opposite appears to be true.

As set out above, AR5 tells us that without additional measures to limit GHGs we are heading for warming of between 2.5 and 7.8 degrees by 2100. Even at the mid-point of this range (about 5 degrees) the consequences are likely to be so severe as to be inconsistent with continuing economic growth at any level. On this crude assessment, the drastic reduction of emissions is the only path available to sustainable growth.

The conclusion is supported by more sophisticated economic analysis.

In 2005, Gordon Brown, then the UK Chancellor, commissioned Nicholas Stern, previously chief economist at the World Bank, to prepare a report on the economics of climate change. The report[16] concluded that unchecked climate change would entail a loss of consumption of between 5% and 20% by 2050; whereas the costs of tackling climate change would be only 1 %.

If the Stern report proved highly controversial, AR5 likewise concludes that the transition to clean energy will support continuing high levels of economic growth.

According to AR5, baselines scenarios for growth in global consumption over the century, ignoring climate change, range from 300% to 900%. Mitigation scenarios likely to limit warming to 2 degrees reduce this by only a small fraction – 3% to 11%. In other words global consumption by 2100 might have grown by 297% instead of a baseline projection of 300%; or 889% instead of a projection of 900%.[17]

Reference to ‘reduced’ growth, does not, of course imply that growth would in fact be greater without the transition. The marginal ‘reduction’ is in relation to an economic model for a world without climate change – i.e. a world contrary to reality.   AR5 states ominously that:

Very little is known about the economic cost of warming above 3 degrees C relative to the current temperature level.[18]

Such scientific circumspection masks the obvious: any predictions of economic growth in the context of average global warming towards the top of the 2.5 to 7.8 degree range risk absurdity. The lower projection of 297% global growth by 2100 (assuming action necessary to limit warming to 2 degrees and the most pessimistic assumption for growth) would, in all probability, represent growth vastly in excess of the alternative of inaction

What changes have occurred to date? | Back to top

Analysis and resources to support the UNFCCC's ultimate objective