Climate change and global warming
Climate change and global warming refer to significant shifts in Earth's climate patterns, predominantly influenced by human activities, particularly since the Industrial Revolution. While climate naturally varies over long periods, current trends are largely attributed to increased greenhouse gas emissions, resulting in global warming. The Intergovernmental Panel on Climate Change (IPCC) emphasizes that this anthropogenic climate change poses serious risks to global security and the environment.
Climate change is measured through various indicators, including rising global surface temperatures and changes in ice mass, with the last decade marked as the warmest on record. Predictions suggest that temperatures may rise between 1.8°C and 4.0°C by the end of the twenty-first century, with more pronounced effects in polar regions. The consequences of these changes include more frequent extreme weather events and shifts in precipitation patterns, which could have devastating impacts on ecosystems and human societies.
Addressing climate change has become a pressing global issue, leading to international agreements like the Paris Climate Agreement that seek to reduce emissions. However, disparities exist, as developing nations, despite contributing less to emissions, often face greater vulnerabilities. This complexity highlights the need for inclusive and equitable responses to climate change, acknowledging the diverse perspectives and experiences of all nations involved.
Climate change and global warming
While Earth’s climate is constantly changing in various ways, the planet tends to experience long-term trends toward either warming or cooling. The potential or actual contribution of postindustrial human activity to climate change, the consequences of that contribution, and the proper response to those consequences remain matters of crucial importance and significant debate.
Terminology
Climate is characterized by mean air temperature, humidity, winds, precipitation, and frequency of over a lengthy period of time, typically at least thirty years. In turn, the term "climate change" refers to long-term, sustained shifts in climate patterns. In the broadest sense, climate change includes both natural trends and anthropogenic (human-caused) changes. One of the best-known and significant examples of climate change is global warming. Indeed, the two terms are commonly used more or less interchangeably, although scientists stress that they are technically distinct.
Although climate changes on longer than millennial timescales are natural, contemporary global warming is mainly anthropogenic, according to the United Nations Intergovernmental Panel on Climate Change (IPCC) and other experts. For this reason, the United Nations Framework Convention on Climate Change (UNFCCC) defines climate change as
a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.
Scientists have increasingly directed attention to anthropogenic climate change, both because it poses a threat to global security and because it can be altered by altering human and governmental behavior.
Context
Earth's climate is a complex and ever-changing system. On scales of millennia to hundreds of thousands of years, the variations in Earth’s orbit directly influence the planet’s climate. This orbit is described by the cyclical variations in Earth’s orbit known as the Milanković cycles, which repeat every 20,000 to 100,000 years. (Beyond the million-year timescale, tectonic drift is likely the main driver of climate change). Based on ice-core proxy data, four major global glaciations occurred in the past 450,000 years, about one every 100,000 years, correlating well with the Milanković cycles. The most recent ice age ended about 11,500 years ago. Over the course of Earth’s history, its temperature has swung more than 10° Celsius between cold and warm modes. Other natural factors that can affect climate change or shorter-term climate variability include Earth’s internal processes, such as volcanic eruptions, and external parameters such as solar luminosity.
In many contexts, however, climate change is understood specifically as the anthropogenic global warming that began around the time of the Industrial Revolution. This is driven primarily by greenhouse gas and aerosol emission and, to a lesser degree, changes in land use. While separating natural and anthropogenic causes of climate change can be challenging, there is strong scientific consensus around anthropogenic climate change. Since no controlled laboratory setting exists in which to conduct climate change experiments, climate scientists have developed computer models based on the laws governing climate systems. By altering model settings, one can simulate natural and anthropogenic effects on climate, separately or in combination, thereby tracing the causes of climate change.
Climate Change Detection
Earth’s atmosphere is chaotic, and weather can change dramatically in a matter of days or even hours. Temperature in some places may rise or fall by 20° Celsius or more in one day. On the other hand, climate, as the average of years of weather conditions, changes on a much smaller scale. For example, the global mean surface air temperature increased by only 0.6° Celsius during the twentieth century. Yet, such a seemingly small increase can have extremely significant effects.
The phenomenon of anthropogenic global warming is mainly detected through measurements of mean surface air temperature, as computed from tens of thousands of weather station records spanning decades. The difficulty of ensuring data continuity in time, uniformity in space, and constancy in observational methods poses serious challenges to climatologists. To discern slight trends amid diverging data, scientists use advanced mathematical tools to synchronize all observations, adjust discontinuities, and filter out local influences such as heat island effects.
Modern climate change has generally been observed with in situ thermometers and, later, with remote sensing devices. Paleoclimate change (change before about 1850) is inferred from proxy climate data. Tree rings can provide evidence of temperature and precipitation history for two to three thousand years, while tiny air bubbles trapped in the Antarctic ice deposits provide data on ice ages hundreds of thousands of years in the past. Pollen and zooplankton cells in river and sea sediments also contain useful proxy climate data.
Detecting climate change depends on individual variables. Temperature change is the most reliable such variable, because its internal variability is small and it is more widely observed than other variables. Long-term precipitation changes are more difficult to discern, because rain- and snowfall vary so greatly from one year to the next. The intensity and frequency of extreme weather events such as hundred-year floods are even more difficult to detect, because these events are rare, so a significant data set must cover many years.
Instrument records from land stations and ships indicate that the global annual mean surface air temperature rose steadily during the twentieth century. The warming occurred more quickly in high latitudes than it did in the tropics. It was also faster over land than it was over the ocean and faster in the Northern Hemisphere than in the Southern Hemisphere. Winters warmed more than did summer, and nights warmed more than did days. Contemporary daily temperature ranges narrowed, precisely because nights have warmed more than have days.
This unprecedented warming trend continued to be observed into the twenty-first century. According to US National Aeronautics and Space Administration (NASA) statistics, between the late nineteenth century and 2021, Earth's average surface temperature rose about 1.9 degrees Fahrenheit. The United Nations reported that the period from 2011 to 2020 was the warmest decade on record to that point. Meanwhile, the years 2005, 2010, 2014, 2015, and 2016 each increased the record for warmest individual year. That record was again broken in 2023, by which time every one of the top-ten warmest years on record had come over the previous decade.
Another indicator used to detect climate change is the mass of sea ice and glaciers. According to NASA, Antarctica lost ice mass by about 151 billion tons each year between 2002 and late 2022, and Greenland lost about 273 billion tons each year during the same period. Such ice loss also contributed to higher measured sea levels. By 2023, global mean sea level had risen 101.2 millimeters (4 inches) since 1993, when modern satellite record-keeping began.
Climate Change Scenario
Future climate changes are predicted by climate models based on assumed greenhouse gas (GHG) emission scenarios. The scenarios range from high fossil fuel consumption, resulting in atmospheric carbon dioxide (CO2) concentration of 800 parts per million, to low consumption, with CO2 concentration reaching 550 parts per million. The reliability of these predictions depends on future global environmental, energy, and climate policy, as well as the accuracy of the models.
Most models project that climate change will accelerate during the twenty-first century and that the global average temperature will increase by between 1.8° Celsius and 4.0° Celsius by 2100. As in the past, warming will be more pronounced in the polar Northern Hemisphere during winter. Precipitation amounts are likely to increase in high latitudes and to decrease in most subtropical lands. Heat waves and heavy precipitation events will very likely increase in frequency. With warmer oceans, future tropical storms will become more intense, with greater peak wind speeds and heavier precipitation.
Perspectives and Response
Modern scientific understanding of Earth's climate began to develop in the nineteenth century, especially with the recognition of the greenhouse effect as a key contributor to atmospheric temperature. Some early researchers even suggested that human activity could impact the greenhouse effect and therefore the global climate. However, it was not until the mid-twentieth century that the contemporary trend of global warming came into focus. Through the late twentieth century and into the early twenty-first, scientists steadily built up evidence that human activity—mainly the burning of fossil fuels—was driving climate change. While these findings often met with considerable political backlash and some climate change skeptics became influential, by the 2010s there was strong expert consensus around anthropogenic climate change.
Increased awareness of climate change also brought growing concern about its impacts. Many scientists warned that if anthropogenic global warming continued unchecked, there would likely be drastic consequences for human society and biodiversity. Pressure to take action on climate change mitigation became a major global political issue, with complex economic and social implications. A number of international agreements overseen by the United Nations Framework Convention on Climate Change (UNFCCC), including the 1997 Kyoto Protocol and 2015 Paris Climate Agreement, sought to build global consensus on fighting climate change and set clear goals for emissions reductions. Many countries also explored their own policies for reducing emissions or otherwise mitigating climate change and its effects. However, such efforts met with mixed results.
There was also growing attention to issues of environmental justice in relation to climate change. On average, developing nations faced greater climate vulnerability than wealthier nations despite being responsible for a far lower amount of greenhouse gas emissions from energy and industry. By the 2020s, the US, Europe (including Russia), and China were responsible for roughly two thirds of all global carbon dioxide emissions since 1750. This disparity led some to argue that wealthier, more developed nations should pay some form of reparations to developing countries impacted by climate change.
Key Concepts
- anthropogenic: caused by human activity
- climate: long-term, average, regional or global weather patterns
- emission scenario: a set of posited conditions and events, involving climatic conditions and pollutant emissions, used to project future climate change
- greenhouse gases (GHGs): trace atmospheric gases that trap heat on Earth, preventing it from escaping into space
- proxy: an indirect indicator of past climate conditions
- weather: the set of atmospheric conditions obtaining at a given time and place
Bibliography
"Global Temperature." NASA, climate.nasa.gov/vital-signs/global-temperature/?intent=121. Accessed 19 Aug. 2024.
Hersher, Rebecca. "Climate Change Makes Heat Waves, Storms and Droughts Worse, Climate Report Confirms." NPR, 9 Jan. 2023, www.npr.org/2023/01/09/1147805696/climate-change-makes-heat-waves-storms-and-droughts-worse-climate-report-confirm. Accessed 29 Sep. 2023.
Lindsey, Rebecca. "Climate Change: Global Sea Level." Climate.gov, 19 Apr. 2022, www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level. Accessed 29 Sep. 2023.
Mélieres, Marie-Antoinette, and Chloé Maréchal. Climate Change: Past, Present, and Future. Chichester: Wiley, 2015. Digital file.
Nakicenovic, N., et al., eds. Special Report on Emission Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change. Cambridge UP, 2000.
Plumer, Brad. "Climate Change Is Speeding Toward Catastrophe. The Next Decade Is Crucial, UN Panel Says." The New York Times, 20 Mar. 2023, www.nytimes.com/2023/03/20/climate/global-warming-ipcc-earth.html. Accessed 29 Sep. 2023.
Tietjen, Bethany. "Many of the World’s Poorest Countries are the Least Polluting but the Most Climate-Vulnerable. Here’s What They Want at COP27." PBS News Hour, 2 Nov. 2022, www.pbs.org/newshour/science/many-of-worlds-poorest-countries-are-the-least-polluting-but-the-most-climate-vulnerable-heres-what-they-want-at-cop27. Accessed 15 Apr. 2023.
"What Is Climate Change?" NASA, science.nasa.gov/climate-change/what-is-climate-change/. Accessed 19 Aug. 2024.
"What Is Climate Change?" United Nations, www.un.org/en/climatechange/what-is-climate-change. Accessed 19 Aug. 2024.
"What Is Climate Change? A Really Simple Guide." BBC News, 8 Feb. 2024, www.bbc.com/news/science-environment-24021772. Accessed 19 Aug. 2024.