Climate change: An introduction

Climate change is the current rapid warming of the Earth’s climate caused by person activity. If left unchecked (and current responses are doing little to halt it) it poses an unprecedented risk to person civilisation and the ecosystems on this planet.

What does it mean to say the climate is changing?

First, ‘climate’ is very not the same as ‘weather’. Weather changes by the hour and, especially in the UK, naturally varies widely between years. We know the climate is changing because, averaged out over longer periods, the global mean temperature has been consistently rising, across land and sea. It is now about 0.8C above pre-industrial times.

The below graph shows global temperatures from 1860 to 2015. The data used came from the National Oceanic and Atmospheric Administration (NOAA). For more information, click the link.

Climate Lab Book created an animated climate spiral, illustrating the increase in global temperatures from 1850 to the present.

The planet is experiencing changes in climates, affecting millions of lives. Already, there has been the bleaching of coral reefs, the sea ice volume in the Arctic has been reaching new lows, an increase in the number of natural disasters worldwide (such as wildifres, droughts, floods) and the mass migration of species. For more information, you are able to read more about the current ramifications of climate change here.

What is the greenhouse effect?

Certain gases in the Earth’s atmosphere (water vapour, CO2, methane and others) allow sunlight to pass through, but then stop the heat from escaping back out into space – much like glass in a greenhouse. Without this, our planet would be uninhabitable to most forms of life. However, by changing the balance of gases in the atmosphere, humans have increased the greenhouse effect, causing the rising temperatures we now see.

Where do greenhouse gases come from?

As explained above, these gases exist naturally in our atmosphere. The most significant increases are in carbon dioxide ( there is now over a third more CO2 in our atmosphere than there was before the industrial revolution) and methane. Methane is a more potent greenhouse gas, but it only remains in the atmosphere for about a decade. Carbon dioxide lasts for about 100 years or more, so even when we stopped emissions from person activities altogether, the planet would continue to warm up from the gases already emitted. The main causes of increased CO2 in the atmosphere are burning fossil fuels (coal, oil and gas), and deforestation and other changes in land use that release stored CO2 and methane.

The below graph, also known as the Keeling Curve, shows CO2 levels today and how this compares with the last 10,000 years.

Is there any doubt about what’s happening?

The idea of an urgent shift away from fossil fuels is not welcome to everybody, and those who seek to delay or prevent this have already been very successful in spreading the idea that climate scientists are uncertain about climate change (or even fraudulent!). Unfortunately there is certainly, as legal terminology has it, no ‘reasonable doubt’ about climate change.

Could the rise in atmospheric carbon be coming from somewhere else?

Humans are currently emitting around 30 billion tonnes of CO2 into the atmosphere every year. Of course, it may be coincidence that CO2 levels are rising so sharply at the same time so let’s look at more evidence that we’re responsible for the rise in CO2 levels:

• When we measure the kind of carbon gathering in the atmosphere, we observe more of the type of carbon that comes from fossil fuels
• This is certainly corroborated by measurements of oxygen in the atmosphere. Oxygen levels are falling in line with the amount of carbon dioxide rising, just as you’d expect from fossil fuel burning which takes oxygen out of the air to create carbon dioxide
• Further independent evidence that humans are raising CO2 levels comes from measurements of carbon found in coral records going back several centuries. These find a recent sharp rise in the type of carbon that comes from fossil fuels

How do we know that the extra CO2 in the atmosphere is warming the planet through the greenhouse effect?

• CO2 absorbs heat at particular wavelengths. Satellites measure less heat escaping out to space, at the particular wavelengths that CO2 absorbs heat, while surface measurements show more heat returning at CO2 wavelengths.
• If an increased greenhouse effect is causing global warming, we should see certain patterns in the warming. For example, the planet should warm faster at night than during the day. This is certainly indeed being observed.
• Another expected result of greenhouse warming is cooling in the upper atmosphere, otherwise known as the stratosphere. This is certainly exactly what’s happening.
• With the lower atmosphere (the troposphere) warming therefore the upper atmosphere (the stratosphere) cooling, another consequence is the boundary between the two layers should rise as a consequence of greenhouse warming. This has also been observed.
• An even higher layer of the atmosphere, the ionosphere, is expected to cool and contract in response to greenhouse warming. This has been observed by satellites.

( The above Q&A was taken from Skeptical Science, where you can read more about the evidence and find the answers to lots more questions like «Could the sun be causing it?» and » What about the Mediaeval warm period?»)

What can we expect to happen next?

That is dependent on what we do now. Because of all the greenhouse gases already in the atmosphere, if the human race died out tomorrow, we’d still expect the planet to continue heating up. If we carry on emitting at the rate we are today, it will heat up a great deal more rapidly. Rather than just warming, it makes more sense to think of it because the climate becoming more unstable, with extra energy in the system. Extreme weather events will become more common, ecosystems is put under stress and so will person agriculture and water supplies. Some parts of the world are particularly vulnerable, such as sub-Saharan Africa, but no area is immune.

The pledges that governments have made so far to cut emissions are insufficient. Even if implemented fully, they’re consistent with an average global temperature rise of 4C (see, e.g. the IEA). However, there are now concerns that global temperatures could rise at a greater rate due to the Earth’s climate sensitivity being non-linear. A rise of 2C has been viewed as a ‘safe limit’ in international negotiations, but this does not fully take into account either the serious humanitarian and ecosystem impacts of this temperature rise in many parts of the world. The poorest countries of the world and small island states face threats, for the latter to their actual existence, with any global warming above 1.5°C. Nor does it consider the risk of triggering positive feedback mechanisms. An example of the latter is the release of frozen carbon and methane from melting in the polar regions, which would further accelerate warming. Since there is in reality no clear ‘safe’ zone, this demands an even more urgent response to cutting emissions.

What would world 4C hotter look like?

• Increases of 6°C or more in average monthly summer temperatures would be expected in large regions of the planet, including the Mediterranean, North Africa, the Middle East, and parts of the United States, with heatwaves raising temperatures further.
• Sea levels would rise by 0.5 to 1 metre at least by 2100, and by several metres more in the coming centuries. Major cities would be threatened by flooding.
• As oceans absorb excess CO2 they would become around 2 1/2 times as acid as they are now, and marine ecosystems would be devastated by this on top of the impacts of warming, overfishing and habitat destruction. Most coral reefs would be long destroyed ( from around 1.4C temp rise)
• As ecosystems undergo rapid transition, mass extinctions are likely.
• Agriculture would be under extreme stress in much of the world, especially the poorest regions.

Read more

There is a vast amount of information on the internet about the science of climate change, from the simple to the deeply technical, and some that is just plain wrong ( find out more about climate helpme .com sceptics). For example, here is a brief introduction to climate science and further discussion of the climate risk.

‘Climate Emergency’, written by the campaign’s former National Coordinator, Phil Thornhill, is a good introduction to important concepts in the science of climate change.

For an explanation of where we are heading, look at the presentation ‘Climate Change: Going Beyond Dangerous’ by Professor Kevin Anderson.

More on the impacts of climate change from the planet Bank: ‘Turn Down the Heat: Why a 4°c warmer world must be Avoided’

Climate change, periodic modification of Earth’s climate brought about as a result of changes in the atmosphere as well as interactions between the atmosphere and various other geologic, chemical, biological, and geographic factors within the Earth system.

A series of photographs of the Grinnell Glacier taken from the summit of Mount Gould in Glacier National Park, Montana, in 1938, 1981, 1998, and 2006 (from left to right). In 1938 the Grinnell Glacier filled the entire area at the image. By 2006 it had largely disappeared from this view.1938-T.J. Hileman/Glacier National Park Archives, 1981 – Carl Key/USGS, 1998 – Dan Fagre/USGS, 2006 – Karen Holzer/USGS
BRITANNICA EXPLORES EARTH’S TO-DO LIST
Person action has triggered a vast cascade of environmental problems that now threaten the continued ability of both natural and person systems to flourish. Solving the critical environmental problems of global warming, water scarcity, pollution, and biodiversity loss are perhaps the greatest challenges of the 21st century. Will we rise to meet them?

The atmosphere is a dynamic fluid that is continually in motion. Both its physical properties and its rate and direction of motion are influenced by a variety of factors, including solar radiation, the geographic position of continents, ocean currents, the location and orientation of mountain ranges, atmospheric chemistry, and vegetation growing on the land surface. Each one of these factors change through time. Some factors, such as the distribution of heat within the oceans, atmospheric chemistry, and surface vegetation, change at very short timescales. Others, such as the position of continents and the location and height of mountain ranges, change over very long timescales. Therefore, climate, which results from the physical properties and motion of the atmosphere, varies at every conceivable timescale.

climate change: timelineA timeline of important developments in climate change.Encyclopædia Britannica, Inc./Patrick O’Neill Riley

Climate is often defined loosely due to the fact average weather at a particular place, incorporating such features as temperature, precipitation, humidity, and windiness. A more specific definition would state that climate is the mean state and variability of these features over some extended time period. Both definitions acknowledge that the weather is always changing, owing to instabilities in the atmosphere. And as weather varies from day to day, so too does climate vary, from daily day-and-night cycles up to periods of geologic time hundreds of millions of years long. In a very real sense, climate variation is a redundant expression—climate is always varying. No two years are exactly alike, nor are any two decades, any two centuries, or any two millennia.

This article addresses the concept of climatic variation and change within the set of integrated natural features and processes known as the Earth system. The nature of the evidence for climate change is explained, as are the principal mechanisms that have caused climate change throughout the history of Earth. Finally, a detailed description is given of climate change over many different timescales, ranging from a typical person life span to all of geologic time. For a detailed description of the development of Earth’s atmosphere, see the article atmosphere, evolution of. For full treatment of probably the most critical issue of climate change in the contemporary world, see global warming.

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The Earth System

The atmosphere is influenced by and linked to other options that come with Earth, including oceans, ice masses (glaciers and sea ice), land surfaces, and vegetation. Together, they make up an integrated Earth system, in which all components interact with and influence one another in often complex ways. For example, climate influences the distribution of vegetation on Earth’s surface ( e.g., deserts exist in arid regions, forests in humid regions), but vegetation in turn influences climate by reflecting radiant energy back into the atmosphere, transferring water (and latent heat) from soil to the atmosphere, and influencing the horizontal movement of air across the land surface.

icebergTourist motorboat in front of a massive iceberg near the coast of Greenland.Paul Zizka/Visit Greenland (Visitgreenland.com)
TurkmenistanDrought-resistant plants grow in the Repetek Preserve in the southeastern Karakum Desert, Turkmenistan.© Rodger Jackman/Oxford Scientific Films Ltd.
Deciduous forest in fall coloration, Wasatch Mountains, Utah.Dorothea W. Woodruff/Encyclopædia Britannica, Inc.

Earth scientists and atmospheric scientists are still seeking a full understanding of the complex feedbacks and interactions among the various components of the Earth system. This effort is being facilitated by the development of an interdisciplinary science called Earth system science. Earth system science is composed of a wide range of disciplines, including climatology ( the study of the atmosphere), geology ( the study of Earth’s surface and underground processes), ecology ( the study of how Earth’s organisms connect with one another and their environment), oceanography ( the study of Earth’s oceans), glaciology ( the study of Earth’s ice masses), and even the social sciences ( the study of individual behaviour in its social and cultural aspects).

A full understanding of the Earth system requires knowledge of how the system and its components have changed through time. The pursuit of this understanding has led to development of Earth system history, an interdisciplinary science that includes not only the contributions of Earth system scientists but also paleontologists (who study the life of past geologic periods), paleoclimatologists (who study past climates), paleoecologists (who study past environments and ecosystems), paleoceanographers (who study the history of the oceans), and other scientists concerned with Earth history. Because different components of the Earth system change at different rates as they are relevant at different timescales, Earth system history is a diverse and complex science. Students of Earth system history are not just concerned with documenting what has happened; they also view the past as a number of experiments in which solar radiation, ocean currents, continental configurations, atmospheric chemistry, and other important features have varied. These experiments provide opportunities to learn the relative influences of and interactions between various components of the Earth system. Studies of Earth system history also specify the full array of states the system has experienced in the past and those the system is capable of experiencing later on.

Definitely, people have always been aware of climatic variation at the relatively short timescales of seasons, years, and decades. Biblical scripture and other early documents refer to droughts, floods, periods of severe cold, and other climatic events. Nevertheless, a full appreciation of the nature and magnitude of climatic change did not come about until the late 18th and early 19th centuries, a time once the widespread recognition of the deep antiquity of Earth occurred. Naturalists of this time, including Scottish geologist Charles Lyell, Swiss-born naturalist and geologist Louis Agassiz, English naturalist Charles Darwin, American botanist Asa Gray, and Welsh naturalist Alfred Russel Wallace, came to recognize geologic and biogeographic evidence that made sense only in the light of past climates radically different from those prevailing today.

Long-term data sets reveal increased concentrations of the greenhouse gas carbon dioxide in Earth’s atmosphereJohn P. Rafferty, biological and earth science editor of Encyclopædia Britannica, discussing carbon dioxide and its relationship to warming conditions at Earth’s surface.Encyclopædia Britannica, Inc.See all videos for this article

Geologists and paleontologists in the 19th and early 20th centuries uncovered evidence of massive climatic changes taking place before the Pleistocene—that is, before some 2.6 million years ago. For example, red beds indicated aridity in regions that are now humid ( e.g., England and New England), whereas fossils of coal-swamp plants and reef corals indicated that tropical climates once occurred at present-day high latitudes in both Europe and North America. Since the late 20th century the development of advanced technologies for dating rocks, together with geochemical techniques and other analytical tools, have revolutionized the understanding of early Earth system history.

The occurrence of multiple epochs in recent Earth history during which continental glaciers, developed at high latitudes, penetrated into northern Europe and eastern North America was recognized by scientists by the late 19th century. Scottish geologist James Croll proposed that recurring variations in orbital eccentricity (the deviation of Earth’s orbit from a perfectly circular path) were responsible for alternating glacial and interglacial periods. Croll’s controversial idea was taken up by Serbian mathematician and astronomer Milutin Milankovitch in the early 20th century. Milankovitch proposed that the device that brought about periods of glaciation was driven by cyclic changes in eccentricity as well as two other orbital parameters: precession (a change in the directional focus of Earth’s axis of rotation) and axial tilt (a change in the inclination of Earth’s axis with respect to the plane of its orbit around the Sun). Orbital variation is now recognized as a important driver of climatic variation throughout Earth’s history (see below Orbital [Milankovitch] variations).

The precession of Earth’s axis.Encyclopædia Britannica, Inc.
Climate change
CAUSES

• Fossil-fuel combustion, deforestation, rice cultivation, livestock ranching, industrial production, and other person activities have increased since the development of agriculture and especially since the start of the Industrial Revolution.
• Greenhouse gases (GHGs) in the atmosphere, like carbon dioxide, methane, and water vapour, absorb infrared radiation emitted from Earth’s surface and reradiate it back, thus contributing to the greenhouse effect.
• Ice sheets, sea ice, terrestrial vegetation, ocean temperatures, weathering rates, ocean circulation, and GHG concentrations are influenced either directly or indirectly by the atmosphere; however, they also all feed back into the atmosphere and influence it in important ways.
• Periodic changes in Earth’s orbit and axial tilt with respect to the Sun (which occur over tens of thousands to thousands and thousands of years) affect how solar radiation is distributed on Earth’s surface.
• Tectonic movements, which change the shape, size, position, and elevation of the continental masses and the bathymetry of the oceans, have had strong effects on the circulation of both the atmosphere and the oceans.
• The brightness of the Sun continues to increase due to the fact star ages and it passes on an increasing amount of this energy to Earth’s atmosphere over time.

OUTCOMES

• Probably the most familiar and predictable phenomena are the seasonal cycles, to which people adjust their clothing, outdoor activities, thermostats, and agricultural practices.
• Person societies have changed adaptively in response to climate variations, although evidence abounds that certain societies and civilizations have collapsed in the face of rapid and severe climatic changes.
• The complex feedbacks between climate components can produce «tipping points» in the climate system, where small, gradual changes in one component of the system can lead to abrupt climate changes.
• The history of life has been strongly influenced by changes in climate, some of which radically altered the course of evolution.

Evidence For Climate Change

All historical sciences share a problem: As they probe farther back in time, they become more reliant on fragmentary and indirect evidence. Earth system history is no exception. High-quality instrumental records spanning the past century exist for most parts of the world, but the records become sparse in the 19th century, and few records predate the late 18th century. Other historical documents, including ship’s logs, diaries, court and church records, and tax rolls, can sometimes be used. Within strict geographic contexts, these sources can provide information on frosts, droughts, floods, sea ice, the dates of monsoons, and other climatic features—in some cases up to several hundred years ago.

Fortunately, climatic change also will leave a variety of signatures in the natural world. Climate influences the growth of trees and corals, the abundance and geographic distribution of plant and animal species, the chemistry of oceans and lakes, the accumulation of ice in cold regions, and the erosion and deposition of materials on https://shmoop.pro Earth’s surface. Paleoclimatologists study the traces of these effects, devising clever and delicate methods to obtain information about past climates. Most of the evidence of past climatic change is circumstantial, so paleoclimatology involves a great deal of investigative work. Wherever possible, paleoclimatologists try to use multiple lines of evidence to cross-check their conclusions. They’re frequently confronted with conflicting evidence, but this, as in other sciences, often leads to a enhanced understanding of the Earth system and its complex history. New sources of data, analytical tools, and instruments are becoming available, and the field is moving quickly. Revolutionary changes in the understanding of Earth’s climate history have occurred since the 1990s, and coming decades will bring many new insights and interpretations.

Greenland: climate changeLearn how scientists collect samples of lake bed sediments in Greenland for use in their investigations of ancient climate change.Courtesy of Northwestern University (A Britannica Publishing Partner)See all videos for this article

Ongoing climatic changes are being monitored by systems of sensors in space, on the land surface, and both on and below the surface of the world’s oceans. Climatic changes of the past 200–300 years, especially since the early 1900s, are documented by instrumental records and other archives. These written documents and records provide information about climate change in some locations for the past few hundred years. Some very rare records date back over 1,000 years. Researchers studying climatic changes predating the instrumental record rely increasingly on natural archives, which are biological or geologic processes that record some aspect of past climate. These natural archives, often referred to as proxy evidence, are extraordinarily diverse; they include, but are not limited to, fossil records of past plant and animal distributions, sedimentary and geochemical indicators of former conditions of oceans and continents, and land surface features characteristic of past climates. Paleoclimatologists study these natural archives by collecting cores, or cylindrical samples, of sediments from lakes, bogs, and oceans; by studying surface features and geological strata; by examining tree ring patterns from cores or sections of living and dead trees; by drilling into marine corals and cave stalagmites; by drilling into the ice sheets of Antarctica and Greenland and the high-elevation glaciers for the Plateau of Tibet, the Andes, and other montane regions; and by a wide variety of other means. Techniques for extracting paleoclimatic information are continually being developed and refined, and new kinds of natural archives are being recognized and exploited.