Understanding Climate Change


The Science: What is Climate Change?
Definitions of climate change:
The Intergovernmental Panel on Climate Change (IPCC)defines climate change as ‘any change in climate over time, whether due to natural variability or as a result of human activity'.
The United Nations Framework Convention on Climate Change (UNFCCC) defines climate change as ‘a change of climate that is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and that is in addition to natural climate variability observed over comparable time periods’. In other words, the UNFCCC uses the term climate change to mean only those changes that are brought about by human induced changes in green house gases (GHGs).
The World Meteorological Organisation (WMO) defines climate change as ‘a statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer). Climate change may be due to natural internal processes or external forcing, or to persistent anthropogenic changes in the composition of the atmosphere or in land use’.
The Intergovernmental Panel on Climate Change (IPCC) concluded in its Synthesis Report 2007, "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (man-made) greenhouse gas concentrations" via the greenhouse effect.
The greenhouse effect causes the atmosphere to trap more heat energy at the Earth's surface and within the atmosphere by absorbing and re-emitting longwave energy. It is a naturally occurring process that results from the fact that certain atmospheric gases, such as carbon dioxide, water vapor, and methane, are able to change the energy balance of the planet by absorbing longwave radiation emitted from the Earth's surface. Without the greenhouse effect life on this planet would probably not exist as the average temperature of the Earth would be a chilly -18° Celsius, rather than the present 15° Celsius.
Since the Industrial Revolution, mankind has been releasing extra quantities of greenhouse gases into the atmosphere, which trap more heat, enhancing the natural greenhouse effect. This is known as the "enhanced" greenhouse effect and is the direct result of human activities. Processes such as the burning of fossil fuels, industrial operations and forest clearing release have increased the amount of carbon dioxide entering the atmosphere.
Carbon Dioxide is the Main Culprit
Emissions from fossil fuel combustion account for about 65% of the extra carbon dioxide now found in our atmosphere. The remaining 35% is derived from deforestation and the conversion of prairie, woodland, and forested ecosystems primarily into agricultural systems. Natural ecosystems can hold 20 to 100 times more carbon dioxide per unit area than agricultural systems.
Average concentrations of atmospheric carbon dioxide in the year 2007 were about 384 parts per million. Prior to 1832, ice core levels of carbon dioxide were about 284 parts per million. Today, we are at 100 ppm (35%) above the 1832 ice core levels of 284 ppm.
Every time we put on the air-con, turn on a light, use a computer, drive our car, watch television or boil the kettle, we are creating carbon dioxide (CO2) . Carbon dioxide has an atmospheric lifetime of between 50 and 200 years. This means that carbon dioxide will be present in the atmosphere for at least 50 years before it is absorbed by a sink or becomes part of another chemical reaction. Consequently, carbon dioxide emitted into the atmosphere today could cause global warming for up to two centuries.
Your cup of tea lasts a very long time!
Methane is Also a Worry
Since 1750, methane (CH4) has doubled, and could double again by 2050. Each year we add 350-500 million tons of methane to the air by raising livestock, coal mining, drilling for oil and natural gas, rice cultivation, and garbage sitting in landfills. It stays in the atmosphere for only 10 years, but traps 20 times more heat than carbon dioxide.
How Exactly has our Climate Changed?
In 2007, the Intergovernmental Panel on Climate Change (IPCC) affirmed that warming of the climate system is unequivocal, with effects such as increasing land and ocean temperatures, rising global average sea level, and reduced snow and ice already being observed. These changes, which are linked directly to human activities producing greenhouse gases, are already causing changes in ecosystems, water supply and availability, and patterns of extreme events, with (in many but not all cases) consequent damages to human health, buildings, livelihoods, and infrastructure.
Climate change isn’t happening in isolation. There are many other factors that interact to cause a specific environmental impact (e.g. decrease in crop yields), including natural variability in weather patterns and local land practices.
When considering climate change impacts, several additional factors should not be ignored:
  • The possibility of some “positive feedback loops” (i.e. thresholds, tipping points) that could accelerate climate change beyond what the climate models currently predict (e.g. thawing of Siberian tundra releasing methane, melting of Greenland glaciers and break-up of the Antarctic ice cap leading to dramatic sea level rise).
  • The prospect of accelerated emissions of GHGs in the foreseeable future due to rapid and substantial economic growth in various parts of the world such as China and India, coupled with population growth.
  • The interactive and knock-on effects between these phenomena in a global economy and Hong Kong’s economy.



i) Temperature Rise

IPCC's Synthesis Report (2007) states that the Earth's surface temperature has risen by 0.74oC over the last one hundred years, and is expected to increase by 1.8oC - 6.4oC by 2100. Changes in snow, ice and frozen ground have with high confidence increased the number and size of glacial lakes increased the number and size of glacial lakes, increased ground instability in mountain and other permafrost regions and led to changes in some Arctic and Antarctic ecosystems. {1.2}
Acacia Trees Burnt©WWF Canon/J E Newby
Increasing global temperature will cause sea level to rise and is expected to increase the intensity of extreme weather events and to change the amount and pattern of precipitation. Other effects include changes in agricultural yields, trade routes, glacier retreat, species extinctions and increases in the ranges of disease vectors. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a thousand years even if greenhouse gas levels are stabilized. The delay in reaching equilibrium is a result of the large heat capacity of the oceans.
Because the atmosphere and ecosystems are extremely complex, and because we don’t know exactly how society will respond, it can be difficult to say precisely what will happen at any given temperature.
Graph per the 16th November 2007 presentation for the IPCC Synthesis Report (2007).Observed changes in (a) global average surface temperature; (b) global average sea level from tide gauge (blue) and satellite (red) data and (c) Northern Hemisphere snow cover for March-April. All differences are relative to corresponding averages for the period 1961-1990. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (a and b) and from the time series (c).
ii) Sea Level Rise

The IPCC's Synthesis Report (2007) states that global average sea level rose at an average rate of 1.8m [1.3 to 2.3] mm per year over 1961 to 2003 and at an average rate of about 3.1 mm per year from 1993 to 2003. Thermal expansion of warming oceans has contributed to about 57% of sea level rise, with decreases in glaciers and ice caps contributing about 28% and losses from the polar ice sheets contributing the remainder.
In the future, one of the most worrisome effects of global warming is its effect on the world’s ice reserves, not only in the Arctic, Antarctic and Greenland, but also on glaciers far from the sea that provide plant, animal and human communities with melt water essential to their survival. For example, a 24-year study by scientists in China stated in 2004 that the total area of China’s glaciers had shrunk by approximately 5.5% since the 1960s. If current warming trends continue, it is estimated that as much as 64% of the glacier mass may be gone by 2050.
As the oceans warm, carbon dioxide solubility in the surface waters decreases markedly. However, the overall system is quite complex.
Source: August 2006 (UTC), Alfred Wegener Institute for Polar and Marine Research
iii) Intensity and Frequency of Precipitation

IPCC observations show that changes are occurring in the amount, intensity, frequency and type of precipitation. Precipitation is the general term for rainfall, snowfall and other forms of frozen or liquid water falling from clouds. Precipitation is intermittent, and the character of the precipitation when it occurs depends greatly on temperature and the weather situation.
iv) Extreme Weather Events have Changed in Frequency

In addition, some extreme weather events have changed in frequency and/or intensity over the last 50 years:
  • It is very likely that cold days, cold nights and frosts have become less frequent over most land areas, while hot days and hot nights have become more frequent. {WGI 3.8, SPM}
  • It is likely that heat waves have become more frequent over most land areas. {WGI 3.8, SPM}
  • It is likely that the frequency of heavy precipitation events (or proportion of total rainfall from heavy falls) has increased over most areas. {WGI 3.8, 3.9, SPM}
  • It is likely that the incidence of extreme high sea level has increased at a broad range of sites worldwide since 1975. {WGI 5.5, SPM} (source: IPCC's Synthesis Report (2007)
The Third Assessment Report also indicated that higher surface temperatures may increase the frequency and severity of extraordinary weather events, such as storms triggered by climatic extremes such as El Niño. Events such as floods and storms have already risen in frequency and intensity since the 1950s, and a recent report by theinsurance industry estimates that losses related to climate change could exceed US$100 billion a year over the next century.
What About Dangerous Climate Change?
The term was legally introduced in the 1992 United Nations Framework Convention on Climate Change (UNFCCC), which calls for stabilization of greenhouse gases to ‘prevent dangerous anthropogenic (man-made) interference with the climate system’ while allowing ‘economic development to proceed in a sustainable manner.’
The point at which climate change becomes very dangerous is not certain, but a 2 °C increase above preindustrial levels is the most commonly accepted level. This requires meeting the IPCC1 scenario which stabilizes C02e at between 445 and 490 ppm. To do this requires an emissions peak by 2015 and a reduction by 2050 of 50% to 85% from year 2000 levels.
Is Dangerous Climate Change the Same as the 'Tipping Point'?
The 'tipping point' is more like 'very' dangerous climate change. The tipping point in is the point at which change due to human activity brings about sufficient new processes in nature to make any human reversal of the change impossible. Some climate scientists believe this will be reached in about 2017, while others, notably James Hansen NASA's top climate scientist, believe it has already been reached.
What is the Prospect for Future Emissions?
The IPCC has developed several sets of scenarios to predict changes in atmospheric CO2 concentrations. IPCC's lowest or most positive scenario looks at CO2e stabilizing between 445 and 490 ppm and temperature between 2°C and 2.4°C. This requires an emissions peak by 2015 and a reduction by 2050 of 50% to 85% from year 2000 levels.
  • Positive Scenario: One IPCC scenario for CO2 emissions over the next 100 years assumes that the human population will only increase by 4 million people. The world's economy will grow by 2.0% per year for the next 25 years and then growth will slow. It also assumes the cost of nuclear power will go down by 0.4% per year. This scenario is the most optimistic. If the assumptions of this scenario are met, CO2 emissions will increase by 1.4 GT in the next twenty-five years. Then CO2 emissions would decrease by 4.2 GT over the following seventy-five years. The emissions of CO2 in the year 2100 will be 4.6 GT. That is 2.8 GT lower than they are today. Under this IPCC scenario, the concentration of atmospheric CO2 in the year 2100 will be 450 ppm.
  • Pessimistic Scenario: The most pessimistic IPCC scenario for CO2 emissions over the next 100 years assumes the human population will increase by 5.3 billion people. The world's economy will grow by 3.0% per year. It also assumes the cost of nuclear power will increase. Under these conditions, CO2 emissions will increase by 7.7 GT in the next twenty-five years, and by another 20.7 GT over the following seventy-five years. Based on these assumptions, the predicted CO2 emissions in the year 2100 will be 35.8 GT. That is nearly five times greater than emissions are today. The concentration of atmospheric CO2 will be 900 ppm.
  • Business As Usual: The most likely IPCC scenario for future CO2 emissions lies between these two extremes. This middle scenario is called scenario "A" or the "business as usual" scenario. It is called the "business as usual" scenario because it assumes that population and economic growth rates, as well as nuclear energy costs, will not change significantly in the future. Based on the assumptions of scenario A, annual emissions of CO2 will rise to 20.3 GT by the year 2100. The concentration of atmospheric CO2 will be 700 ppm. This is double today's concentration.
Note: It is important to recognise that much of the change in climate in our atmosphere over the next 30 to 40 years has already been determined by historic emissions and because of the inertia in the climate system. Therefore it is vital to adapt to some degree of climate change whether or not future emissions are reduced.
From the IPCC scenarios there have been other significant forecasts.
  • IEA: The IEA World Energy Outlook 2004 predicts that CO2 emissions will increase by 63% over 2002 levels by 2030. This is generally consistent with the IPCC emission scenarios, published in 2000. This means that the world will, in the absence of urgent and strenuous mitigation actions in the next 20 years, almost certainly be committed to a temperature rise of between about 0.5°C and 2°C relative to today by 2050.

    Much of the increase in these emissions is expected to occur in the developing world where emerging economies, such as 
    China and India, fuel economic development with fossil energy. Developing countries’ emissions are expected to grow above the world average at 2.7 percent annually between 2001 and 2025; and surpass emissions of industrialized countries near 2018.
World Carbon Dioxide Emissions by Region, 2001-2025
(Million Metric Tons of Carbon Equivalent)
Stern Review
The forecasts for the economic cost of climate change in Sir Nicholas Stern’s review are based on stabilising emissions at 550 parts per million in the atmosphere of CO2 and its equivalent gases (ppm CO2e). But the narrative in his report draws on a wide range of studies and concludes that this level – an effective doubling of CO2 over pre-industrial levels – carries an unacceptably high risk of exceeding 2°C of global warming. Throughout the review, Stern considers the implications of stabilizing within a range between 450 and 550ppm CO2e. But even at 450ppm stabilisation, there is a risk in excess of 50% of exceeding 2°C. These are not encouraging odds.
IETA Greenhouse Gas Market Report 2010

GHG 2010 Market Report Cover


This 2010 GHG Market Report, “Post Copenhagen and Climate Policy: Where Global Emissions Trading Goes from Here”, covers a wide variety of topics and regions and is more comprehensive than ever. Articles in this year’s Report cover the current challenges and the development of emissions trading systems spanning the globe. Any reader’s understanding of the state of global carbon markets will broaden after reading this report

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