Environmental Impacts

Global annual surface temperatures
 relative to 1951-1980 mean temperature.
Source: NASA Goddard Institute for Space Studies

Observable changes have already occurred due to the increased concentration of greenhouse gases in the atmosphere.  Average global surface temperatures have risen by about 0.6°C and sea levels have risen during the past century.  Satellite data shows large decreases in glaciers, ice caps, and polar ice sheets. Precipitation trends have been changing worldwide, increasing in some regions and decreasing in others.  There may also be a higher frequency of extreme weather events, such as heat waves and tropical cyclones.  Many of these changes will inevitably continue due to the current amount of greenhouse gases in the atmosphere.  The only uncertainty is to what degree:  if global greenhouse emissions continue to rise, then global temperatures and sea levels will likely rise at a higher rate.


A Threat to Biodiversity
Although climate change itself may not currently be the largest threat to biodiversity, it has already had ecological impacts that cause changes in species populations.  

• Many species ranges are shifting towards the poles and to higher elevations (Walther 2002).
• Spring activities such as breeding have occurred progressively earlier since the 1960s (Dunn & Winkler 1999, Walther 2002).
• Specialists are experiencing population declines and extinction due to vulnerability to environmental changes and increased competition with generalists (Walther 2002).
• Species adapted to warm weather are flourishing in some regions, while species adapted to cold weather are experiencing population declines (Walther 2002).
• Rises in sea level are causing some coastal species to contract (Harley 2006).
• Changes in the abundance, distribution, and behavior disrupts the way species normally interact with each other through competition, predation, and parasitism (Parmesan 2006). 
• Disturbances associated with climate change, such as flooding, drought, and ocean acidification pose a threat to a wide variety of species (Harley 2006).

These general, large-scale impacts have serious consequences for global biodiversity.  Climate change is causing changes in population dynamics and posing selective pressures on many species that simply cannot adapt quickly enough to these changes.  Combined with other human impacts, such as population fragmentation, pollution, overexploitation, and the introduction of exotic species, climate change is becoming a serious threat to a wide variety of taxa and species.

A Threat to Human Health and Life
Climate change does not only pose a threat to ecosystems, but is expected to have large-scale impacts on human health.  A recent assessment from the World Health Organization (WHO) reported that climate change may now lead to at least 5 million cases of illness and over 150,000 deaths every year.  According to WHO, diseases that effect poor countries such as malaria, diarrhea and malnutrition are sensitive to climate. Increased cases of these diseases combined with the higher frequency of extreme climate events is creating serious risks to human health and survival, especially in many developing countries.

The two maps below show regions where people are most likely to be affected by climate change.  The first map shows vulnerability to desertification, where red areas are the most vulnerable.  The second map estimates vulnerability to a variety of factors affected or exacerbated by climate change, such as sea-level rise, development, availability of natural resources, agricultural dependency and conflict.  Areas of darker blue indicate high vulnerability, while areas of light green indicate low vulnerability.

Countries such as India, Bangladesh, Nepal, Mozambique, Afghanistan, Zimbabwe, Madagascar, Myanmar, and Ethiopia are at the highest risk of experiencing the negative effects of climate change.  Much of Sub-Saharan Africa will be severely affected.  Many of these countries are among the least developed in the world, limiting their capability to cope with the effects of climate change.  Although they are not large producers of greenhouse gases, people living in these areas may suffer the worst consequences of them (Maplecroft Global Risks, WHO, McMichael 2010).

Source: USDA-NRCS.  Click to enlarge.

Source: Maplecroft Global Risks