Climate Change: The Greatest Threat

Climate change is a broad term used to refer to changes in the Earth’s climates, at local, regional, or global scales, and can also refer to the effects of these changes. In recent decades, the term ‘climate change’ is most often used to describe changes in the Earth’s climate driven primarily by human activity since the pre-Industrial period (1850 onwards), particularly the burning of fossil fuels and removal of forests, resulting in a relatively rapid increase in carbon dioxide concentration in the Earth’s atmosphere.

Global warming is a term often used interchangeably with climate change, as it is one of the most important measures of global changes. Global warming refers to the rise in average global temperatures, which is linked to significant impacts on humans, wildlife, and ecosystems around the world. Because there are more factors and impacts than only rising surface temperatures, the term climate change is used to include these additional impacts. The concentration of carbon dioxide in the atmosphere has risen from hovering around 280 parts per million (ppm) in pre-Industrial time, to 413 ppm as of early 2020. This concentration of carbon dioxide is unprecedented in recorded history. Scientists have reported that we need to return to a ‘safe’ concentration of 350 ppm by 2100 in order to stabilize global warming.

The planet is warming, from North Pole to South Pole. Since 1906, the global average surface temperature has increased by more than 1.6 degrees Fahrenheit (0.9 degrees Celsius)— even more in sensitive polar regions. And the impacts of rising temperatures aren’t waiting for some far-flung future–the effects of global warming are appearing right now. The heat is melting glaciers and sea ice, shifting precipitation patterns, and setting animals on the move.

Scientists already have documented the impacts of climate change:

• Ice is melting worldwide, especially at the Earth’s poles. This includes mountain glaciers, ice sheets covering West Antarctica and Greenland, and Arctic sea ice. In Montana's Glacier National Park, the number of glaciers has declined to fewer than 30 from more than 150 in 1910.
• Much of this melting ice contributes to sea-level rise. Global sea levels are rising 0.13 inches (3.2 millimeters) a year, and the rise is occurring at a faster rate in recent years.
• Rising temperatures are affecting wildlife and their habitats. Vanishing ice has challenged species such as the Adélie penguin in Antarctica, where some populations on the western peninsula have collapsed by 90 percent or more.
• As temperatures change, many species are on the move. Some butterflies, foxes, and alpine plants have migrated farther north or to higher, cooler areas.
• Precipitation (rain and snowfall) has increased across the globe, on average. Yet some regions are experiencing more severe drought, increasing the risk of wildfires, lost crops, and drinking water shortages.
• Some species—including mosquitoes, ticks, jellyfish, and crop pests—are thriving. Booming populations of bark beetles that feed on spruce and pine trees, for example, have devastated millions of forested acres in the U.S.

Other effects could take place later this century, if warming continues. These include:

• Sea levels are expected to rise between 10 and 32 inches (26 and 82 centimeters) or higher by the end of the century.
• Hurricanes and other storms are likely to become stronger. Floods and droughts will become more common. Large parts of the U.S., for example, face a higher risk of decades-long "megadroughts" by 2100.
• Less freshwater will be available, since glaciers store about three-quarters of the world's freshwater.
• Some diseases will spread, such as mosquito-borne malaria (and the 2016 resurgence of the Zika virus).
• Ecosystems will continue to change: Some species will move farther north or become more successful; others, such as polar bears, won’t be able to adapt and could become extinct.

The decisions we make on carbon emissions over coming decades will affect our climate for a long time to come, as emissions will profoundly impact the rate of future climate change, particularly after 2030. Even if emissions of greenhouse gases are reduced to near zero during this century, we will have to live with a warmer climate for centuries.

For those parts of the climate system that respond slowly, such as the deep ocean, ice sheets and permafrost, change will continue for a long time. Many associated impacts—such as sea-level rise— and processes that exacerbate climate change—such as releases of methane and CO2 from thawing permafrost soils—will continue long after emissions are stopped. The impacts of climate change will not be evenly felt around the world – people living in the poorest countries and in geographically vulnerable regions (such as small-island states) will be first and most significantly impacted. This is because communities living in poverty are more likely to be exposed to environmental hazards, are often more dependent on natural resource-based livelihoods such as agriculture, and have fewer resources to cope with climate impacts.

Each fractional degree of warming also results in outsized impacts on biodiversity and species extinction, and disturbances in natural ecosystems. Even if carbon emissions in the atmosphere can be absorbed and stabilized over a long period of time, many of the impacts on wildlife, land, water, and people will be irreversible once they occur, which makes halting the release of greenhouse gas emissions, and limiting global warming as much as possible, the first priority.

It may not be too late to avoid or limit some of the worst effects of climate change. Recycling and driving more fuel-efficient cars are examples of important behavioral change that will help, but they will not be enough. Because climate change is a truly global, complex problem with economic, social, political and moral ramifications, the solution will require both a globally-coordinated response (such as international policies and agreements between countries, a push to cleaner forms of energy) and local efforts on the city- and regional-level (for example, public transport upgrades, energy efficiency improvements, sustainable city planning, etc.). It’s up to us what happens next.