Science of Climate Change – Carbon Foresight

The scientific community has reached a strong consensus regarding the science of global climate change. The world is undoubtedly warming. This warming is largely the result of emissions of carbon dioxide and other greenhouse gases from human activities including industrial processes, fossil fuel combustion, and changes in land use, such as deforestation.

Visible light from the sun passes through the atmosphere and is absorbed by the Earth's surface - some of that energy is then emitted back to the atmosphere as heat. Greenhouse gases trap that heat, which would otherwise be released into space, raising the temperature of the atmosphere and, subsequently, the Earth's surface. Increases in greenhouse gases from human activities increase the amount of heat trapped by the atmosphere causing global warming and climate change.

Carbon is used as a shorthand for the greenhouse gases we emit into the atmosphere – is linked with almost all of an organization’s activities, and is present in its supply chain, processes, premises, and ultimately in the products and services it produces.

Water vapor - Water vapor contributes the most to the greenhouse effect and occurs in the atmosphere as a result of the natural cycle of water

Carbon dioxide (CO2) - Carbon dioxide also cycles naturally between the atmosphere and living organisms. Plants and algae remove CO2 from the atmosphere via photosynthesis, while all living things release CO2 via respiration (i.e., breathing). Carbon dioxide also cycles back and forth between water on the Earth's surface (freshwater and the oceans) and the atmosphere. In addition to these natural processes, humans release large quantities of CO2 to the atmosphere by burning fossil fuels, deforestation, and other industrial processes.

Methane (CH4) - Methane is a natural byproduct of decomposition, but significant quantities are also produced via agriculture and animal husbandry as well as by fossil fuel production.

Nitrous oxide (N2O) - Nitrous oxide is released naturally from terrestrial soils and oceans, but substantial quantities are also generated from the use of nitrogen fertilizers in agriculture and through some industrial processes.

Other gases - A number of other natural and man-made gases also contribute to the greenhouse effect, including tropospheric ozone, and industrial gases such as halocarbons.

Aerosols - Aerosols are airborne particles within the atmosphere. Some aerosols, such as sulfate aerosols and black carbon aerosols are also produced by fossil fuel combustion. Sulfate aerosols tend to reflect incoming solar radiation, cooling the Earth's surface. Black carbon aerosols absorb, rather than reflect, solar radiation, which shades the Earth's surface, but warms the atmosphere.

"Global warming" refers to the increase of the Earth's average surface temperature, due to a build-up of greenhouse gases in the atmosphere. "Climate change" is a broader term that refers to long-term changes in climate, including average temperature and precipitation.

Climate varies naturally over both short and long time-scales, but natural climate variability can be distinguished from human-caused climate change.

Scientists have conducted a number of studies that compare observed changes in the global climate with those factors that are known to influence climate. These studies indicate that the climate change observed over the 20th century is due to a combination of changes in solar radiation, volcanic activity, land-use change, and increases in atmospheric greenhouse gases. Of these, greenhouse gases appear to be the dominant driver of climate change over the past few decades.

Globally, surface air temperatures increased by approximately 1 degree F during the 20th century. Some regions of the world have experienced much greater warming; Alaska and the Antarctic peninsula, for example, have warmed by approximately 4 degrees F over the same time period. Other regions of the world, such as the oceans of the Southern Hemisphere and the interior of Antarctica, have not experienced warming.

The observed warming over the 20th century was accompanied by a 10% increase in precipitation in the Northern Hemisphere and an increase in global sea-level of 4-8 inches.

Projections of future changes in climate are typically based on three sources of information:

- Knowledge of historical climate variability and change

- Scientific understanding of the climate system

- Computer models of the climate system that generate projections of future climate based

upon a number of variables

Of these three, climate models have received considerable attention. A number of different models exist and each represents the climate in a different way, resulting in large differences among models in projections of future climate change.

A number of current models do a reasonable job of simulating past climate variability (decades to centuries), but all such models perform poorly at modeling short-term climate variability (days-years) and regional climate variability.

The projections of climate models are also highly dependent upon the assumptions used regarding future trends in greenhouse gas emissions and atmospheric concentrations.

The latest Intergovernmental Panel on Climate Change projections for 21st century average global temperature increase is 2.5 - 10.4 degrees F, based upon multiple climate models and multiple assumptions regarding future greenhouse gas emissions.

Regional warming may be greater or less than the global average. For example, temperature increases in the United States are projected to be approximately 30% higher than the global average. The Arctic is likely to experience the greatest warming.

Associated with this warming will be an increase in global average sea level of 4-35 inches, depending on the magnitude of warming.

Global precipitation patterns will also be altered by temperature increases. Generally, the hydrological cycle is expected to accelerate leading to increases in precipitation at the global level. However, these global increases may not necessarily balance the increased evaporation under warmer conditions, and some regions may experience a decrease in precipitation.

Species in natural ecosystems will attempt to migrate with the changing climate, but will differ in their degree of success. Ecosystem productivity may decrease or increase, at least over the short-term.

Increases in temperature and changes in precipitation will have significant impacts on water resources, either reducing or increasing water availability along with increasing the risk of floods or droughts.

Coastal developments will experience additional sea-level rise that will interact with coastal storms to erode beaches, inundate land, and damage structures.

U.S. agriculture and forestry will likely experience mixed results with moderate warming, with increases in productivity likely in northern states and possible declines in southern states. However, at higher magnitudes of warming, the risk of more uniform adverse effects across the nation increases.

Human health may be affected by climate change through a number of mechanisms including extreme temperatures (i.e., heat waves), exacerbation of air pollution, severe weather, and increased spread of infectious diseases.

Current atmospheric concentrations of greenhouse gases are projected to increase global temperatures by an additional 1oF in coming decades. Thus some degree of continued climate change is inevitable, despite efforts to reduce greenhouse gas emissions, but emissions reductions will aid in reducing the magnitude of that change and stopping human-induced increases in global temperatures.

In order to stop temperature increases, greenhouse gases in the atmosphere must be stabilized, meaning emissions of these gases must be reduced to such a level that they do not cause any additional increase in atmospheric concentrations.

The magnitude of emissions reductions necessary to achieve such stabilization depends on a number of factors including the level at which greenhouse gases should be stabilized and future patterns of fossil fuel use and emissions.

In its latest assessment report the Intergovernmental Panel on Climate Change estimated the magnitude of emissions reductions necessary to stabilize atmospheric concentrations of CO2 at a doubling of the pre-industrial by the end of the century level for a broad range of scenarios for future greenhouse gas emissions. Given mid-range baseline projections for CO2 emissions, IPCC estimated that global CO2 emissions would have to be reduced by the end of the 21st century to 40-75% below baselines.