Science of Climate Change

1. How are the terms climate change, global warming, and global change different?  The term climate change is often used as if it means the same thing as the term global warming. According to the National Academy of Sciences, however, “the phrase ‘climate change’ is growing in preferred use to ‘global warming’ because it helps convey that there are [other] changes in addition to rising temperatures.” Climate change refers to any distinct change in measures of climate lasting for a long period of time. In other words, “climate change” means major changes in temperature, rainfall, snow, or wind patterns lasting for decades or longer. Climate change may result from:
   
   • natural factors, such as changes in the Sun’s energy or slow changes in the Earth’s orbit around the Sun;
   • natural processes within the climate system (e.g., changes in ocean circulation);
   • human activities that change the atmosphere’s makeup (e.g, burning fossil fuels) and the land surface (e.g., cutting down forests, planting trees, building developments in cities and suburbs, etc.).
   Global warming is an average increase in temperatures near the Earth’s surface and in the lowest layer of the atmosphere. Increases in temperatures in our Earth’s atmosphere can contribute to changes in global climate patterns. Global warming is probably the most talked about climate change we are experiencing, but is just one of many changes along with precipitation levels, storm intensity, etc. Global warming can be considered part of climate change along with changes in precipitation, sea level, etc. Global change is a broad term that refers to changes in the global environment, including climate change, ozone depletion, and land-use change.
2. What is the greenhouse effect? The Earth’s greenhouse effect is a natural occurrence that helps regulate the temperature of our planet. When the Sun heats the Earth, some of this heat escapes back to space. The rest of the heat, also known as infrared radiation, is trapped in the atmosphere by clouds and greenhouse gases, such as water vapor and carbon dioxide. If all of these greenhouse gases were to suddenly disappear, our planet would be 60ºF (33ºC) colder and would not support life as we know it. Human activities have enhanced the natural greenhouse effect by adding greenhouse gases to the atmosphere, very likely (greater than 90 percent chance) causing the Earth’s average temperature to rise. These additional greenhouse gases come from burning fossil fuels such as coal, natural gas, and oil to power our cars, factories, power plants, homes, offices, and schools. Cutting down trees, generating waste and farming also produce greenhouse gases.
3. Are human activities responsible for the warming climate? Intergovernmental Panel on Climate Change (IPCC) scientists believe that it is very likely (greater than 90 percent chance) that most of the warming we have experienced since the 1950s is due to the increase in greenhouse gas emissions from human activities.
   


4. How do scientists predict future climate change? The Earth’s climate is very complex and involves the influences of air, land, and oceans on one another. Scientists use computer models to study these interactions. The models project future climate changes based on expected changes to the atmosphere. Though the models are not exact, they are able to simulate many aspects of the climate. Scientists reason that if the models can mimic currently observed features of the climate, then they are also most likely able to project future changes.
5. How much will the Earth warm if emissions of greenhouse gases continue to rise? If humans continue to emit greenhouse gases at or above the current pace, we will probably see an average global temperature increase of 3 to 7°F (2 to 4ºC) by 2100, and greater warming after that. Temperatures in some parts of the globe (e.g., over land and in the polar regions) are expected to rise even more.
   Even if we drastically reduce greenhouse gas emissions, returning them to year 2000 levels and holding them constant, the Earth would still warm about 1°F (0.6ºC) over the next 100 years. This is due to the long lifetime of many greenhouse gases and the slow cycling of heat from the ocean to the atmosphere.
6. Is our planet warming? Yes. The global temperature record shows an average warming of about 1.3°F (0.74ºC) over the past century. According to the National Oceanic and Atmospheric Administration (NOAA), seven of the eight warmest years on record have occurred since 2001. Within the past 30 years, the rate of warming across the globe has been approximately three times greater than the rate over the last 100 years. Past climate information suggests the warmth of the last half century is unusual in at least the previous 1,300 years in the Northern Hemisphere. The Intergovernmental Panel on Climate Change (IPCC) concluded that warming of the Earth’s climate system is now “unequivocal” (i.e., “definite”). The IPCC bases this conclusion on observations of increases in average air and ocean temperatures, melting of snow and ice, and average sea level across the globe.