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The year 2013 provided more clarity about human-generated climate change than ever before. On 27 September 2013, the UN Intergovernmental Panel on Climate Change (IPCC) released the Working Group 1 contribution to its Fifth Assessment Report (AR5), which looks at the science of climate change. It is categorical in its conclusion: climate change is real and man is the main cause. 

The release of the first instalment of AR 5 came in the wake of an unusual number of severe weather-related disasters, and at the head of an almost unbroken series of the hottest years on record, with the period 2000 to 2009 the warmest decade on record so far.  

There are some basic well-established links:

• The concentration of greenhouse gases in the earth’s atmosphere is directly linked to the average global temperature on Earth; 
• The concentration has been rising steadily, and mean global temperatures along with it, since the time of the Industrial Revolution; and
• The most abundant greenhouse gas, carbon dioxide, is the product of burning fossil fuels. 

Greenhouse gases occur naturally and are essential to the survival of humans and millions of other living things, through keeping some of the sun’s warmth from reflecting back into space and making Earth livable. But it’s a matter of scale. A century and a half of industrialization, including clear-felling forests and certain farming methods, has driven up quantities of greenhouse gases in the atmosphere. As populations, economies and standards of living grow, so does the cumulative level of GHG emissions.

AR5 part 1 took stock of where we are and what we now know. For the first time, Working Group 1 could provide a comprehensive assessment of sea level rise, and its causes, over the past few decades. It was also able to estimate cumulative CO2 emissions since pre-industrial times and provide a CO2 budget for future emissions to limit warming to less than 2 degrees C. About half of this budget was already emitted by 2011!

Thanks to the IPCC, this is what we know:

• From 1880 to 2012, average global temperature increased by 0.85°C. To put this into perspective, for each 1 degree of temperature increase, grain yields decline by about 5 per cent. Maize, wheat and other major crops have experienced significant yield reductions at the global level of 40 megatonnes per year between 1981 and 2002 due to a warmer climate.
• Oceans have warmed, the amounts of snow and ice have diminished and sea level has risen. From 1901 to 2010, the global average sea level rose by 19 cm as oceans expanded due to warming and ice melted. The Arctic’s sea ice extent has shrunk in every successive decade since 1979, with 1.07 million km² of ice loss every decade.
• Given current concentrations and on-going emissions of greenhouse gases, it is likely that by the end of this century, the increase in global temperature will exceed 1.5°C compared to 1850 to 1900 for all but one scenario. The world’s oceans will warm and ice melt will continue. Average sea level rise is predicted as 24 - 30cm by 2065 and 40-63cm by 2100. Most aspects of climate change will persist for many centuries even if emissions are stopped. 

On 28 March 2014, the IPCC published the Working Group II report on impacts, adaptation and vulnerability. The Working Group III report outlining options to curb greenhouse gas emissions will be released on 11 April 2014. The final synthesis report, an overall summary for policy makers, is due in October, shortly before the UN Climate Change Conference in Lima, Peru. These reports give governments tools that will help design the architecture and content of the 2015 agreement and the assessment of the long-term global goal.

The Summary for Policy Makers, the Technical Summary, as well as the full report of the AR5 Working Groups I and II are available on the IPCC website.

What we know we don’t know, and what we don’t know we don’t know

But, these days, it is what we don’t know that is the most worrying— because you can’t properly prepare for what you can’t foresee. Knock-on effects of even small changes in many natural systems show just how delicate a balance nature strikes.

Scientists talk about “tipping points”, where a gradual change suddenly moves into a self-fuelling spiral. How much methane is trapped in the melting permafrost and in sea-beds in a warming ocean, and, if some or all of that methane is released, what effect will it have on the global temperature and climate? If the ice cover in the poles keeps shrinking so that there is less bright white surface and more dark liquid sea surface, how much more heat from the sun will the dark surface trap, and how much less can the ice packs reflect back into space? Sea mass expands when warm— how much will this add to sea level rise?

Each of these is among the simplest examples of potential vicious cycles identified by scientists.

There is also another unknown. At some point, bright children ask questions about electricity, light and heat, and, inevitably, "where does oil come from?". The simple answer is that, hundreds of thousands of years ago, before humans, the animals and plants that died accumulated on the bottom of water bodies, mixing with sand and mud. Sediment kept piling over the top of that, and the heat and pressure eventually transformed into oil, petroleum or natural gas. These are trapped in porous layers in the earth, prevented from escaping by a non-porous layer of rock.

That's the leading scientific theory on that, in any case. And no one has the definite answer on whether the world's oil reserves will, eventually, run out.

Right now, coal, oil and natural gas power the economies of the world; almost all modern human endeavour produces carbon dioxide. This makes climate change extremely complex, tied up in other difficult issues such as poverty, economic development and population growth. Clearly, dealing with climate change is not easy. It is not about to get any easier. But ignoring it would be worse.

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It’s a familiar story if you grew up reading Rachel Carson’s Silent Spring on the devastating effects of DDT or lived under the widening hole in the ozone layer. You may have felt a sense of déjà vu as the world woke up to an environmental problem - and came together to take action.

Climatologists were the first to sound the alarm in the 1960s and 1970s. These scientists noticed that concentrations of CO2 in the atmosphere were increasing, and that it was correlated to a steady increase in global temperatures. Ice core research backed up this observation, and anecdotal evidence - which had long been trickling in from scientists in many disciplines, farmers and fishermen, as well as amateur nature observers and enthusiasts— began to add up.

More than two decades after these first urgent calls, governments created the United Nations Framework Convention on Climate Change. As far as international agreements went, negotiation of the Convention was fast - especially one on such a vastly complex issue. It was ready for signature at the Earth Summit (formally known as the 1992 United Nations Conference on Environment and Development in Rio de Janeiro).

What led to the creation of the UNFCCC was the first assessment report of the Intergovernmental Panel on Climate Change, released in 1990. The Panel was created by the World Meteorological Organization and the United Nations Environment Programme in 1988, and this first report reflected the views of 400 scientists. Its primary message: global warming was happening and something had to be done about it.

The most recent assessment report currently available is AR4, released in 2007. This is a sample of the observations in AR4 that finally propelled climate change into popular consciousness.

• Snow cover. Since 1978, annual average Arctic sea ice has shrunk, with larger and larger decreases in summer observed each decade. Mountain glaciers and snow cover, on average, have declined in both hemispheres.
• Rain and drought. Since the Industrial Revolution, there have been significant changes in precipitation patterns globally - it now rains much more in eastern parts of North and South America, northern Europe and northern and central Asia, but less in the Sahel, Mediterranean, southern Africa and parts of southern Asia. Globally, the area affected by drought is likely to have increased since the 1970s.
• A hotter world. Over the past 50 years, cold days, cold nights and frosts have become less frequent over most land areas, and hot days and hot nights, more frequent.
• Extreme weather. An increase in intense tropical cyclone activity in the North Atlantic has been observed since about 1970. Warm air is fuel for cyclones and hurricanes.
• The seasons. Spring events come earlier and plants and animals are moving upwards and polewards because of recent warming trends.
• Nature. Scientists have observed climate-induced changes in at least 420 physical processes and biological species or communities.

The IPCC now has a well-established role. It reviews worldwide research, issues regular assessment reports, and compiles special reports and technical papers. Its findings reflect global scientific consensus and are apolitical in character, providing a crucial counterbalance to the often highly charged political debate over how to respond to climate change. Its assessment reports now reflect the work and observations of thousands of scientists.

IPCC reports are frequently used as the basis for decisions made under the Convention. They played a major role in negotiations leading to the Kyoto Protocol.

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Scientists, economists, political scientists, financial experts and all manner of other researchers use historical observations and known links to create models and project outcomes. The IPCC collates published and reviewed science, including projections of what is to come based on a scale of warming scenarios. These collective projections paint quite a clear picture.

On a worldwide level:

• Agricultural yields are expected to drop in most tropical and sub-tropical regions (and in temperate regions, too) if the temperature increase is more than a few degrees. They will be affected, for example, by changing river flows (from ice pack behavior) and rainfall patterns, to the changing behavior of pests, of friendly species required for pollination and pest-control, of the effectiveness of herbicides.
• Diseases, especially those carried by vectors like mosquitoes, could spread to new areas in the world. Imagine what happens when a disease is introduced to a population with no previous contact and therefore little to no immunity to it. Many mosquito species, such as those which carry malaria and dengue, survive and breed more efficiently in hotter temperatures. Then there is increased risk of heatstroke and food-related illnesses.
• Millions of people are expected to be exposed to increasing water stress as ice packs that feed melt-water into rivers that keep millions of people alive, shrink progressively over the decades; or pump extra water into the rivers in the summer, causing damaging, unprecedented flooding.
• More intense weather-related disasters combine with rising sea levels and other climate-related stresses to make the lives of those living on coastlines, particularly the world’s poor, misery. Computer models predicting more “extreme weather events” have in the last decade proven to be on target.
• Extinctions are expected from the current warming trends. Large numbers of plant and animal species, already weakened by pollution and loss of habitat, probably will not survive the next 100 years.

The IPCC has detailed sections on various regions of the world: Africa, Asia, Australia & New Zealand, Europe, Latin America, North American, the Poles, and Small Islands. Please click on the IMPACTS MAP to access the projected impacts on your region.

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