Climate Impacts in Northern Arizona

Rate of Change

Over the course of Earth's history the climate has changed many times, experiencing climactic shifts from unbearably cold ice ages to periods of intense heat and drought. Today, it is not the fact that the climate is changing that is so alarming, but the rate at which this change is taking place and the fact that 97% of scientists agree humans are the primary cause.

In the past, changes in Earth's climate have happened over long periods of time, which gives time for its inhabitants to adapt. In instances when abrupt changes have occurred, they have been accompanied by mass extinctions or drastic changes to Earth's environment.

What is causing the change?

The changing climate is linked to rising concentrations of greenhouse gases such as carbon dioxide, methane and hydrofluorocarbons (HFCs) in the atmosphere, which insulate the planet and cause it to warm. It has been shown that reducing these heat-trapping gas emissions will reduce the speed at which the planet is warming, thus mitigating the expected threats to communities and the environment.

Over the past 50 years, humans have been adding carbon dioxide to the atmosphere at an alarming rate and the temperature has been rising:

Caption: Global annual average temperature (as measured over both land and oceans) has increased by more than 1.5°F (0.8°C) since 1880 (through 2012). Red bars show temperatures above the long-term average, and blue bars indicate temperatures below the long-term average. The black line shows atmospheric carbon dioxide (CO₂) concentration in parts per million (ppm). While there is a clear long-term global warming trend, some years do not show a temperature increase relative to the previous year, and some years show greater changes than others. These year-to-year fluctuations in temperature are due to natural processes, such as the effects of El Niños, La Niñas, and volcanic eruptions. 

Figure source: updated from Karl et al. 2009.

Climate models are used to predict the future climate based on the dynamics of the climate system and trends in carbon emissions. Reducing carbon emissions can greatly decrease global warming, as seen below. This is why it is important that we reduce emissions now.

Increased temperatures have significant effects on weather systems, leading to an expected increase in extreme weather events including heat waves, drought, and fires. Warmer temperatures also mean larger and more ferocious hurricanes in coastal regions, downpour events, and flooding. Visit the National Climate Assessment website for more details.

Caption: Maps show projected change in average surface air temperature in the later part of this century (2071 to 2099) relative to the later part of the last century (1970 to 1999) under a scenario that assumes substantial reductions in heat trapping gases (B1) and a higher emissions scenario that assumes continued increases in global emissions (A2). (See Appendix 3: Climate Science, Supplemental Message 5 for a discussion of temperature changes under a wider range of future scenarios for various periods of this century).

Figure source: NOAA NCDC / CICS-NC