National Aeronautics and Space Administration

What are the consequences of change in the earth system for human civilization?

Earth's climate system has been remarkably stable over the last 20,000 years or so. Human civilization developed in that time span, and our world's average temperature warmed by about 5°C to the temperature it is today. This fact points to one of climate scientists' main concerns about global warming: the temperature is rising faster than at any other time in the history of human civilization and such rapid climate change is likely to seriously stress some populations who cannot adapt quickly enough to the changes.

There will be consequences as the globe warms, and these consequences depend upon the magnitude of the change. There will be both good and bad consequences as some populations may benefit from a warming globe even as others suffer from it. For example, farmers in some latitudes will experience a longer growing season, which may improve crop yields. However, scientists also observe for intense downpours of rain, causing floods, interspersed with longer periods of drought. So such erratic swings in the weather caused by global warming could negatively impact farmers' crop yields.

The warming will cause significant erosion of coastlines as sea level rises due to the heat-driven expansion of the ocean and the influx of freshwater runoff due to melting ice sheets and glaciers. This problem is serious because about 10 percent of the world's population lives in coastal areas level than 10 meters (30 feet) above sea level.

Arctic sea ice will continue to decline until we see a completely ice-free Arctic Ocean; some scientists say this could happen as soon as the year 2040. While this loss of Arctic ice may benefit commercial shipping due to the opening of the northwest passage, other species such as polar bears could face extinction.

A warming climate is likely to shift the ranges of certain types of invasive species (such as undesired weeds, Africanized bees, and fire ants) and infectious diseases (such as West Nile Virus, hantavirus, malaria, etc.). Access to clean freshwater will become more scarce and water resource manager predict that water rights and water management issues will become the most common reason for legal battles and military conflicts among developing nations.

There are costs associated with strategies for addressing global warming, and there are costs associated with failing to address global warming. It seems likely that the costs of failing to address global warming will be far greater in the long run (say by 2100). So any investments humans make today to slow the pace of global warming will pay dividends in the long run by helping to mitigate the problem while keeping it more economically manageable.

Since greenhouse gases are long-lived, the planet will continue to warm for the next several decades even if we stop or reduce emissions today. But the degree to which global warming will happen and change life on Earth depends upon our decisions today.