Scientists from around the world are striving to better understand our climate system. This is no easy task - it is an intricate system, with mechanisms and relationships that both function and impact on local and global scales. In the next few centuries, the possibility exists that the world will undergo climate change at a rate unprecedented in history, with significant impacts on a global scale. The world community must continue to support scientific bodies and institutions involved in climate research. If there is a lapse in our support, there is the potential that certain human activities in the present may irrevocably alter the state of our planet’s climate in a manner that will decrease the quality of life for the entire world population in the future.

Climate change is not a new phenomenon. The global climate has changed in the past and it will change in the future. There is plenty of evidence from the past in glaciers, in rock sediment and strata, and within the landscapes upon which we live today. There are trends that have been observed and documented that provide true knowledge of some of the mechanisms driving the earth’s climate. We know that climate change occurs because of internal variability in the climate system and natural external factors such as volcanic eruptions. However, only recently have we begun to consider how human activities may be affecting the global climate. All statements in this section are based on scientific observations declared in the 3rd Report of the Intergovernmental Panel on Climate Change, Working Group 1. The following has been observed:

• There has been a 0.6°C increase in global mean surface temperature over the 20th century. This represents the largest increase in temperature of any century in the last 1000 years.
• In the lowest 8 km of the atmosphere, temperatures have risen over the last 4 decades
• There has been a decrease in snow cover and ice extent in North America
• The global average sea level has risen 0.1-0.2m in the last century.
• Global ocean heat content has increased over the last five decades. In recent decades, the intensity and frequency of droughts has increased in parts of Asia and Africa.

Greenhouse gases prevent heat from escaping into space by reabsorbing it and radiating it back into the climate system. For that reason, they provide what has been termed the greenhouse effect. Before the industrial revolution, the concentrations of greenhouse gases in the atmosphere were, for the most part, relatively constant over short time scales, only showing significant changes over longer time scales. However, in the last 250 years, atmospheric greenhouse gas concentrations have been increasing at a very high rate of change. This is a result of industrialization and modified land use.

• Carbon dioxide concentrations have increased 31% since 1750. The current concentration in the atmosphere has not been exceeded during the past 420,000 years, and possibly not during the past 20 million years. Current concentrations are increasing at the fastest rate on record in the last 20,000 years.
• Methane concentrations have increased 151% since 1750. Nitrous oxide concentrations have increased 17% since 1750.
• There has been a decrease in CFC concentrations since 1995 likely due to the effects of the Montreal Protocol and its amendments. There has been an increase in concentrations of the gases used to replace CFCs, which are also greenhouse gases.

Carbon dioxide is the most significant greenhouse gas in our atmosphere. Although the positive radiative forcing associated with carbon dioxide is not as strong as other greenhouse gases on a molecule-to-molecule basis, it is the most abundant and by volume alone is the predominant factor associated with warming the planet. A carbon ‘sink’ is a term applied to entities that are able to convert carbon dioxide and store it in alternate forms, effectively removing it from the atmosphere. For example, forests remove carbon dioxide from the atmosphere through photosynthesis and respiration, and store it in alternate carbon forms. Therefore, forests are termed as being carbon ‘sinks’. Oceans act in a similar manner as forests through their ability to absorb carbon dioxide through the ocean-atmosphere gas exchange. Human activities such as deforestation remove carbon sinks, while other human activities such as reforestation create them. Global deforestation in the 20th century has resulted in a net loss of the earth’s ability to convert and store atmospheric carbon dioxide. Scientists are currently studying whether the warming of the oceans is having an effect on their ability to store carbon dioxide.

Interpreting the significance of these observations is a difficult task, but scientists believe that it is very unlikely (indicating a 1-10% chance) that the observed changes in our global climate in the last 100 years is due to internal variability in the climate system. In other words, they believe that human activities are having an affect on the global climate. Great efforts are being made by scientists to better understand the fundamental relationships that exist within our global climate system. On the premise that human activities are responsible for the observed warming trend, it is crucial for us to understand what lies ahead in our future. Climate models based on our current understanding of the global climate system predict that by the year 2100, the global mean temperature is projected to increase by 1.0 to 5.8°C and global mean sea level is projected to rise by 0.09 to 0.88m, the range being caused by differing scenarios of greenhouse gas concentrations in the atmosphere, and global land use. It is very likely that the rate of temperature increase will be higher by the year 2100 based on current projections. In the northern hemisphere, snow cover and sea-ice extent are projected to continue to retreat. There are some general changes in the extremes of climatic events that scientists believe are probable (66-99% chance of occurring) in the next century:

• Increases in tropical cyclone peak wind and precipitation intensities in susceptible areas
• Increased continental drying during the summer and risk of drought in the mid-latitudes
• Intensified precipitation events in all land areas
• Higher maximum and minimum temperatures, and a decrease in frost days in all land areas

Antarctica holds 70% of the world’s fresh water supply (in ice) and accounts for approximately 90% of the worlds ice. Antarctic ice is important to scientific research because much of the evidence we have gathered on climate change in the past has come from ice samples collected from Antarctica. Past atmospheric gas concentrations have been preserved in air pockets in the ice sheets, glaciers and ice shelves. These records date back hundreds of thousands of years providing scientists with evidence of previous climates, and the state and composition of their atmospheres. Glacial sediments on the sea floor around Antarctica provide evidence of the advance and retreat of ice sheets as was caused by different climates in the past. Essentially, much of what we know today about climate change in the past would not have been made possible without scientific research in Antarctica. It is also being affected by climate change today.

Over the past 50 years, Antarctica has warmed in some areas and cooled in others. On average, the Antarctic climate does not appear to have changed significantly. However, regional changes have been observed, in particular a warming of 2.5°C in the Antarctic Peninsula region. This increase in temperature is well in excess of the current global mean rate of 0.6°C/ century. The warming in this region is believed to be responsible for the collapse of the Larson A and Wordie ice shelves. In the spring of 2002, the Larson B ice shelf (3250 km2) also disintegrated. Due to the fact that these ice shelves are already floating, there was no direct change in sea level. What is unknown at the moment is the relationship between the floating ice shelves and the continental ice sheets and glaciers. Research is currently being done to determine if the absence of ice shelves can destabilize continental ice resulting in increased ice-flow into the ocean. That in effect, could result in an increase in sea level. However, the areas in which this would be of particular concern i.e. western Antarctica, are well away from the peninsula region, and currently have much colder climates. Western Antarctica is grounded below sea level. However, it is unclear whether increasing surface and ocean temperatures might result in the loss of grounded ice leading to a substantial rise in global sea level. More research is required so that scientists may better understand the dynamics of the western Antarctic ice sheet.

To learn more about the impact of humans on the global climate, please visit the Intergovernmental Panel on Climate Change website at http://www.ipcc.ch/ .