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The year 2007 marked a new and disturbing global realisation. The world learnt that year that climate change was human-made, definitely happening, and that the collective global effort so far to keep greenhouse gases to a “safe” level was grossly insufficient.

The Intergovernmental Panel on Climate Change (IPCC) had released its Fourth Assessment Report (AR4), 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. Any child under the age of 10 in 2007 was part of this worrying global trend: almost every year he or she had lived on Earth had been among the hottest in living record.

These 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.

AR4 took stock of where we are and what we now know. Thanks to the IPCC, here's a quick snapshot of what we know:

The average temperature of the earth’s surface has risen by 0.74°C since the late 1800s. It is expected to go up another 1.8°C to 4°C by the year 2100 if no action is taken. That’s a fast and intense change in geological time. Even if it “only” gets another 1.8°C hotter, it would be a larger increase in temperature than any century-long trend in the last 10,000 years.

• About 20-30% of plant and animal species is likely at higher risk of extinction if the global average temperature goes up by more than 1.5 to 2.5°C. 
• Nine of the last 10 years were the hottest years on record, according to the United States’ National Oceanic and Atmospheric Administration (NOAA). 2005 and 2010 tied for first place. In second place was 1998. 
• The average sea level rose by 10 to 20 cm over the 20th century. An additional increase of 18 to 59 cm is expected by the year 2100. Higher temperatures cause ocean volume to expand. Melting glaciers and ice caps add more water. And as the bright white of ice and snow give way to dark sea green, less and less rays from the sun are reflected back into space, intensifying the heating.

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-fueling 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 endeavor 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, and 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 the 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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