Global Impacts of Climate Change

The mass media have made much of the fate of polar bears in the Arctic due to losses of summer sea ice. Although melting sea ice and glaciers and drowning bears are some of the widely known early warning signs of change, they are not the only things that tell us something is awry with the global climate.

(Top) Patterns of linear global temperature trends over the period 1979 to 2005 estimated at the surface (left), and for the troposphere from satellite records (right). Grey indicates areas with incomplete data.

(Bottom) Annual global mean temperatures (black dots) with linear fits to the data. The left hand axis shows temperature anomalies relative to the 1961 to 1990 average and the right hand axis shows estimated actual temperatures, both in °C. Linear trends are shown for the last 25 (yellow), 50 (orange), 100 (purple) and 150 years (red). The smooth blue curve shows decadal variations, with the decadal 90% error range shown as a pale blue band about that line. The total temperature increase from the period 1850 to 1899 to the period 2001 to 2005 is 0.76°C ± 0.19°C.

In some northern latitudes, growing seasons are longer because spring now arrives earlier than before and bird nesting and animal migration patterns have changed. Some species of insects, like butterflies, dragonflies and beetles, are surviving at higher latitudes than before. Some species more commonly associated with warmer climates, like loggerhead turtles, are increasingly being spotted in the United Kingdom.

These changes in climate cues are linked to changes in weather patterns, particularly changes in temperature and precipitation. Single abnormalities in weather are not the things that tell us that climate change is occurring. On their own, an unseasonably cool December in Bermuda or a wetter than usual summer in the Chagos Islands could be random events, but evidence of climate change comes from observed patterns over time.

Some of the IPCC conclusions about observed global trends are below.

Temperature: Eleven of the 12 warmest years since 1850 (when instrumental record keeping began) occurred between 1995 and 2006. The linear warming trend over the last 50 years, an average of 0.13°C per decade (with a range between 0.10°C and 0.16°C), is nearly double that of the previous 100 years. The total temperature increase from 1850–1899 to 2001–2005 is an average of 0.76°C, with a range between 0.57°C and 0.95°C (IPCC, 2007).

In their Fourth Assessment Report, the IPCC concluded it is very likely that 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 have become more frequent. It also suggests heat waves may have become more frequent over most land area and there are possibly more heavy precipitation events over most areas (IPCC, 2007). 

Source IPCC, 2007b, p.111 FAQ 5.1

Time series of global mean sea level (deviation from the 1980-1999 mean) in the past and as projected for the future. For the period before 1870, global measurements of sea level are not available. The grey shading shows the uncertainty in the estimated long-term rate of sea level change. The red line is a reconstruction of global mean sea level from tide gauges and the red shading denotes the range of variations from a smooth curve. The green line shows global mean sea level observed from satellite altimetry. The blue shading represents the range of model projections of the Special Report on Emissions Scenarios (project  A1B) for the 21st century, relative to the 1980 to 1999 mean, and has been calculated independently from the observations. Beyond 2100, the projections are increasingly dependent on the emissions scenario. Over many centuries or millennia, sea level could rise by several metres.

Precipitation: Between 1900 and 2005, there was an increase in precipitation in some parts of the world and a decline in others. There were significant increases in eastern parts of North and South America, northern Europe and northern and central Asia but decreases in the Sahel, the Mediterranean, southern Africa and parts of southern Asia. More areas seem to be affected by drought globally since the 1970s (IPCC, 2007). In future, Arctic and Equatorial regions may become wetter, and subtropical regions drier. However, projections of precipitation changes for temperate regions are less consistent.

Storms:  Since 1970, there has been more intense tropical storm activity, marked by a 75 per cent increase in the number of category 4 and 5 hurricanes.  The largest increases were in the North Pacific, Indian and Southwest Pacific Oceans, but the number of hurricanes in the North Atlantic has also been above normal in nine of the past 11 years, including the record breaking 2005 season (IPCC, 2007). One of the natural factors that helps decrease storm intensity is cold ocean waters, but as average ocean temperatures increase (see below), a natural retardant is becoming an accelerant.

Sea level and temperature: Global average sea level has risen at an average rate of 1.8 mm per year since 1961, with a marked acceleration in the rate of increase to an average of 3.1 mm per year since 1993.  It is too soon, however, to know if the latter is a short-term variability or a long-term trend.  Sea level rise is the consequence of two processes associated with warming: inflows of water from melting glaciers, ice caps and the polar sheets and thermal expansion of seawater, that is, an increase in the volume of seawater in response to a temperature change.

Snow and ice extent:  Satellite data since 1978 show that annual average Arctic sea ice extent has shrunk by an average of 3.7 percent per decade, with larger decreases in summer of 7.4 per cent per decade. Mountain glaciers and snow cover on average have declined in both hemispheres.

Bermuda

The Caribbean

British Indian Ocean Territory

Mediterranen

South Atlantic

South Pacific