Earth’s climate system is made up of five interactive components: the atmosphere (air), the hydrosphere (liquid water), the cryosphere (frozen water), the lithosphere (the soil and rocks of the planet’s crust), and the biosphere (the living world). Together, these five elements harness the life-giving power of solar energy, while at the same time creating a responsive system capable of maintaining sufficient resources for life. 1 2
Today, however, the whole system is being destabilized by global warming, which is causing huge ecological damage, loss of habitat and spread of disease, as well as rapidly rising temperatures and the threat of major sea level rise, with existential implications for coastal communities around the world.
- How Does The Atmosphere Affect The Climate System?
- What Part Does The Hydrosphere Play?
- How Ocean Currents Affect The Climate System
- The Global Conveyor Belt
- Does Global Warming Affect Deep Ocean Currents?
- The Cryosphere
- How Does The Cryosphere Affect The Climate System?
- What Is The Impact Of Global Warming On The Cryosphere?
- What Role Does The Lithosphere Play In The Climate System?
- How Does the Biosphere Affect The Climate System?
- What External Forcings Influence The Climate System?
- How Does The Climate System Deal With External Forcings?
- Can The Climate Cope With Man-Made Global Warming?
How Does The Atmosphere Affect The Climate System?
Earth’s atmosphere consists of a layer of gases (mostly nitrogen and oxygen) that we call “air”, kept in place around the planet by the force of gravity. Roughly 50 percent of the total mass of the atmosphere is compressed into the first 5km (18,000 feet) of the atmosphere (the troposphere). This includes nearly all the water vapor and moisture in the air, hence it is here that most of Earth’s weather takes place.
The atmosphere is also the largest and most rapidly traversable part of the planet, and acts as a major highway for a large number of essential processes, such as: the greenhouse effect; the hydrological, carbon and nitrogen cycles, photosynthesis, acid rain, ocean-atmosphere exchange of CO2, and the like.
The atmosphere contributes to the climate system in four main ways.
- First, it maintains a cosy surface temperature of around 15°C (59°F) thanks to the “Greenhouse Effect” – an insulating mechanism which prevents heat from escaping into space. Without this thermal insulation, the surface temperature would be a frosty minus 18°C (roughly the temperature of the North Pole).
The greenhouse effect works like this. When sunlight reaches the Earth, about 29 percent is reflected back into space. The remaining 71 percent is absorbed by the Earth’s air, land and sea. According to the laws of physics, this incoming energy must be balanced by an equivalent amount of outgoing energy. Therefore, the Earth radiates the same amount of energy back into space. However, some of this radiated heat is trapped and absorbed by certain gases (water vapor and carbon dioxide are the most abundant) and re-radiated back to Earth. It is this trapped heat that drives the natural greenhouse effect and that makes life as we know it, possible. For more on this, see: Earth’s Energy Balance.
- Second, the atmosphere redistributes incoming solar heat in order to help balance out the energy differences across the globe. These energy differences stem from the fact that the Equator receives more heat than higher latitudes, notably the polar regions where sunlight strikes the surface at a much lower angle. The atmosphere helps to reduce these variations in temperature by transporting heat from the warm tropics to the cooler polar regions, in a series of three circular air convection movements.
It works like this. Warm air at the equator rises. When it reaches an altitude of 10-15 km (6-9 miles), it flows away from the equator, towards the poles. At about 30° latitude it cools and falls to the ground, where some of it rises once again and follows a similar loop until about 60° latitude, when once again it falls to the ground. A third similar movement takes it to the pole.
If the Earth didn’t rotate and cause the Coriolis Effect (a pull to the right, northwards – a pull to the left, southwards), only one large movement of air would be necessary between the equator and the poles. But because the Earth does rotate, three movements are needed both north and south of the equator.
- Third, atmospheric circulation has a significant effect on patterns of precipitation which – along with temperature – is a defining feature of a region’s climate. Along the Intertropical Convergence Zone, an area near the equator where northeast and southeast trade winds converge, the cooling of warm and moist surface air during its rising motion causes heavy rainfall. Likewise, the vital summer monsoon in India (June-September), which provides more than three quarters of the country’s annual rainfall, is caused by heat differences between the warmer land and cooler ocean, leading to a change in the usual wind direction.
- Fourth, the atmosphere exerts a major influence on the climate system through the formation of clouds. Aside from their precipitation, clouds affect climate in two opposing ways. On the one hand, they absorb heat radiating upwards from the Earth’s surface (a cloudy night is a warmer night), thus contributing to the greenhouse effect. On the other hand, they are quite effective at reflecting incoming sunlight, thus exerting a cooling effect. (On average, clouds tend to have a small cooling effect on climate.) For more on this, see: How Do Clouds Affect Climate?
What Part Does The Hydrosphere Play?
The ocean – which accounts for roughly 97.5 percent of the hydrosphere and covers 71 percent of the planet – is the largest absorber of solar energy on the planet. This unique ability to store heat over long periods of time accords the ocean a vital role in stabilizing Earth’s climate system. (See also: How Do Oceans Influence Climate?)
According to the IPCC’s Special Report on the Ocean and Cryosphere in a Changing Climate (September 2019), the ocean has absorbed over 90 percent of the excess heat in the climate system, resulting in a 200 percent increase in the rate of ocean warming around the world. 3
The main reason why the ocean is such an effective heat and CO2 buffer, is because it’s a liquid that is being constantly mixed and moved by waves, tides, and currents, carrying heat and CO2 from the tropics to the poles and back. For more, see: Effects of Global Warming on Oceans.
Regional Weather Systems in the Tropics
Regional weather cycles – such as the Indian Ocean Dipole (IOD) and the El Nino-Southern Oscillation (ENSO) in the Pacific – are driven by differences in sea surface temperature (SST). It’s one way for the enormous heat absorbed by the oceans to make itself felt. These weather systems are capable of causing devastating damage to ecosystems on land and sea.
How Ocean Currents Affect The Climate System
Not unlike the atmospheric circulation system, ocean currents help to disperse heat around the globe by transporting warm water to the Arctic and Antarctic, and cold polar water to the Indian and Pacific Oceans. There are two basic types of ocean circulation: surface and deep-water currents.
Surface currents make up only 8 percent of the water and account for only 10 percent of ocean currents. They are found on or near the surface of the sea, down to a maximum depth of about 400 m (1,300 ft). They are driven largely by wind and can be relatively fast-moving (250 cm/sec, or 5.5 mph). Surface currents are warmer and are the main carriers of heat. The Gulf Stream, for example, brings tropical warmth to the coasts of the UK and northwestern Europe.
Warm tropical surface water provides most of the power for hurricanes and cyclones. It also provides power for regional weather systems such as El Nino/La Nina and the Indian Ocean Dipole. These systems have a huge influence on drought and floods at opposite ends of the Pacific and Indian Oceans, respectively.
By contrast, deep ocean currents account for roughly 90 percent of currents and travel much more slowly (from 2-10 cm/sec, or 1-4 in/sec). Furthermore, deep currents (like the Antarctic Circumpolar Current) are colder and driven mainly by density (which depends on temperature and salinity) – a process known as thermohaline circulation.
Deep currents take cold water from the poles to the equator, thus exerting a cooling effect on the overheated tropics. In addition, in cold water areas they absorb large amounts of carbon dioxide from the atmosphere, which they distribute throughout the oceans. Lastly, as they move slowly along the ocean floor, they collect the nutrient-rich remains of decayed plant and animal matter that accumulate in the depths, which in due course they bring to the surface, creating a feeding frenzy involving almost the entire marine food web, from phytoplankton to whales.
Given that phytoplankton are estimated to be responsible for 85 percent of the oxygen in the world, this replenishment of the ocean surface water with large amounts of nutrition is a major contribution to climate chemistry.
The Global Conveyor Belt
Oceanographers have identified a global-scale system of ocean currents (dubbed the “global conveyor belt” by geoscientist Wally Broecker), that snake around the world transporting water from the equator to both polar regions and from the poles to the tropical seas. It includes surface, mid-level and deep-water currents, and scientists estimate that it takes water about 1,000 years to complete the entire global loop.
Let’s follow it from the equator, where the surface current known as the Gulf Stream – along with its extension known as the North Atlantic Drift – carries warm water from the tip of Florida up past Ireland and Scotland, towards the Arctic. By the time it arrives in the Norwegian-Greenland Sea, all its heat has evaporated and it has become extremely cold. It then mixes with the freezing salty waters close to areas of sea ice, becoming denser and heavier until it sinks to the ocean floor. Other cold water moves to fill the empty space and it too sinks, initiating the thermohaline current.
The sinking water – now called North Atlantic Deep Water – forms a slow-moving deep-water current which flows all the way to the Antarctic at a depth of between 1500 and 4000 metres. When it arrives in the Southern Ocean it joins the eastward-moving Antarctic Circumpolar Current, a gigantic current that circles the continent of Antarctica. Here, it rises to the surface, pulled by the upwelling effect of strong coastal winds, caused by the Ekman divergence.  At the same time, other freezing water in the Antarctic Circumpolar Current is downwelling in polynyas and below the ice shelf, in the nearby Weddell Sea (off northwest Antarctica), and Ross Sea (off south Antarctica). 4 5
This sinking water now known as Antarctic Bottom Water (AABW), joins the Antarctic Circumpolar Current (ACC) before dividing into two. The first part soon leaves the ACC and turns northwards into the Indian Ocean, while the other travels past New Zealand before looping up into the north Pacific. The Indian Ocean branch upwells south of the Indian sub-continent; the Pacific branch upwells north of the Hawaiian Ridge. Remaining on the surface, the two branches are reunited in the southern Indian Ocean. From here, they round the tip of Africa before returning to the Caribbean, where the circuit recommences.
Does Global Warming Affect Deep Ocean Currents?
Yes. It seems so. The IPCC’s Special Report on the Ocean and Cryosphere stated that the Atlantic meridional overturning circulation (AMOC) was very likely to weaken over the 21st century, as a result of climate change, but was very unlikely to collapse – although it stated it was “physically-plausible.” 5
The cryosphere is the name given to the Earth’s store of frozen water. It includes glaciers, snow cover, sea ice, ice sheets and permafrost. Snow cover extends across 46 million square kilometers (about 17.8 million square miles) of Earth’s surface, of which 98 percent is in the Northern Hemisphere. Sea ice covers about 25 million square kilometers (9,652,553 square miles) of the earth 6, while permafrost is estimated to occupy roughly 22.8 million square kilometers (8.8 million square miles), and this doesn’t include submarine areas.
The Antarctic Ice Sheet covers an area roughly 14 million square kilometers (5.4 million square miles) in size, the equivalent of the contiguous United States and Mexico combined. The Greenland Ice Sheet covers about 1.7 million square kilometers (656,000 square miles), or three times the size of Texas. Climate scientists calculate that if the Greenland Ice Sheet melted, sea level would rise about 7.2 metres (24 feet). 7
How Does The Cryosphere Affect The Climate System?
Snow and ice are vital elements in the climate system, influencing surface heat, the Earth’s energy balance, the temperature of the atmosphere and hydrosphere, precipitation, CO2 distribution, and sea levels.
- To begin with, they exert an important cooling effect on the atmosphere and the oceans, through the air and sea currents described above. In particular, the thermohaline circulation depends entirely upon freezing, salty polar water to create the density that drives the downwelling process in polar seas.
- Ice and snow have a bright reflective surface with a high “albedo“. Because of this, about 80 percent of the sunlight that falls on polar ice is immediately reflected back into space, thus helping to keep global temperatures stable. Conversely, when ice melts, more sunshine gets through and the Earth gets warmer, which results in more ice melt, and so on. This is one of the Planet’s climate feedbacks that boosts global warming. In the Arctic it is known as the Arctic Amplification.
A recent study conducted by a team of U.S. scientists, using satellite data from 1982 to 2014, confirmed that the Arctic was warming up to three times faster than the global average. It also found that, during this period, the surface albedo effect in the Arctic fell by 1.25-1.51 percent per decade due almost entirely to melting ice, while the effect of soot absorption was minimal. 8
- The vast area of Arctic permafrost stores an estimated 1,400 billion tonnes of carbon as methane and methane hydrates. At least one study has warned that 50 billion tonnes of this store could be released abruptly “at any time”, boosting the concentration of methane in the planet’s atmosphere by a factor of twelve. 9
- The global cryosphere, with its vast ice sheets and its 198,000 glaciers, is really a gigantic reservoir of frozen water. Antarctica alone contains enough ice to raise global sea levels by as much as 58 meters (190 ft). If even 2 percent of it melted, it would raise levels by 4 feet: sufficient to swamp half the houses in Miami.
What Is The Impact Of Global Warming On The Cryosphere?
- West Antarctica has been experiencing ice losses for decades. For example, since the 1980s, the Thwaites glacier alone has suffered a net loss of over 600 billion tons of ice. 10 Furthermore, several studies have warned about the possible instability of the West Antarctic ice sheet. Certain glaciological processes such as ice cliff failure and hydro fracture, might, for instance, trigger a collapse of the Thwaites Glacier within a few decades. 11 12
- East Antarctica, long considered the stable part of the continent, was recently discovered to have shed ice every year since 1979. 13
- Empirical evidence – such as, a 60-fold increase in ground slumps from 1984 to 2013 in one area of Canada, alone – indicates that areas of permafrost (a huge reservoir of methane and CO2) across the Arctic are thawing, even in winter, due to a combination of raised temperatures, greater incidence of Arctic fires, and heavy winter snowfall trapping summer heat in the ground. 14
An estimated 6.4 trillion tonnes of methane are trapped in Arctic deposits of methane clathrate on the deep ocean floor. 15 In 2008 the U.S. Department of Energy singled out clathrate destabilization in the Arctic as one of the most credible triggers for sudden climate change. 16
What Role Does The Lithosphere Play In The Climate System?
The lithosphere – the rigid, solid outer layer of the Earth – acts as the interface between the planet’s surface and the geological depths. It plays an important role in the planet’s climate system through its influence on the lithification process – the conversion of sediments into sedimentary rock – although its impact is felt over geological time periods, as the following examples demonstrate.
- Lithification Of Fossil Fuels
The lithosphere has been instrumental in allowing the formation of fossil fuels, like coal, that originated millions of years ago in the form of partly decayed trees and plants from primeval swamps and wetlands. This vegetation sank into the pedosphere and gradually became compacted, forming concentrated seams of carbon-rich organic material which later turned into peat and ultimately coal.
Likewise, petroleum and natural gas, except scientists believe they originated not as vegetation in swamps but as plankton and plant debris in the sediments of coastal marine basins and inland seas. If they had been used sparingly, these carbon-rich deposits, locked away inside sedimentary rock, would have been a highly useful source of energy, especially during an ice age.
- Lithification Of Carbon Dioxide
Through the process of chemical weathering of exposed rock surfaces (via carbonic acid rainfall), the lithosphere – in combination with the hydrosphere – sequesters large quantities of CO2 contained in calcified marine sediments, which over millions of years turn into carbonate sedimentary rocks like limestone. In this way, the lithosphere helps to limit global warming and stabilize temperatures. It also preserves a stock of CO2 for future warming, if necessary. Chemical weathering has a negative feedback effect, since the more CO2 that is emitted into the atmosphere, the more acid rain there will be. And the more acid rain that falls, the more rocks are weathered and the more CO2 is locked up in the slow carbon cycle.
- The Pedosphere
An important part of the lithosphere is the thin surface layer known as the pedosphere. This consists of fine particles of (weathered) rock augmented with moisture-retaining humus and other organic debris, collectively known as soil. Although it only accounts for about 10 percent of Earth’s surface, soil is is a vital natural resource for any ecosystem. Soils hold essential water for plants to make use of during photosynthesis, without which few living things would survive. In addition, they are an essential highway in the recycling of biochemical nutrients like carbon, nitrogen, phosphorus and sulfur, as well as the ecological platform for biomes like tropical rainforests and the taiga. (See also our articles on: The Nitrogen Cycle and The Phosphorus Cycle.)
- Albedo Effect Of Land Surface
The type of plants and vegetation covering the surface has a critical influence on the Earth’s climate system. To begin with it has a major impact on the albedo effect of the land. Vegetation invariably has a lower albedo (lower albedo means less sunlight is reflected) than soil, and a much lower albedo than deserts. Without any tall vegetation, snow can blanket the whole area, resulting in a highly reflective surface area with a high albedo.
- Effect Of Land On Hydrological Cycle
The type of land cover also has a clear influence on the water cycle, as water storage is greater in soils covered by vegetation than on bare land, precipitation often leads to run-off. Water stored in the soil can later be taken up by plant roots and re-emitted into the atmosphere by transpiration, as in the Amazon Rainforest, where water evaporating from the Atlantic is recycled several times within the Amazon biome before it falls as heavy rain as it meets the Andes.
Numerous characteristics of Earth’s climate system are affected by geographical topography. Mountains, for instance, such as the Himalayas, Andes or the Rockies are formidable barriers to the winds that influence the climate on a continental scale. At the same time, the distance to a coastline can affect the temperature and aridity of an area or region. The topography of the sea bed can also have a profound effect on the direction, volume and speed of deep-water thermohaline currents. The shape of an ice sheet or glacier is often a reflection of the underlying bedrock.
How Does the Biosphere Affect The Climate System?
The biosphere (the “living planet” consisting of all the Earth’s animals, plants and other life) influences Earth’s climate system in a wide variety of ways. Here is a short selection.
• Plants and marine phytoplankton remove carbon dioxide (CO2) from the air via photosynthesis. Because CO2 is a greenhouse gas, its removal helps to reduce the greenhouse effect and exerts a cooling influence on climate. However, because photosynthesis needs sunlight, this CO2 removal process stops at sundown. Microbes like bacteria and viruses also play an important role in the ‘biological pump’ which locks up CO2 in the ocean depths. See: Marine Microbes Drive the Aquatic Food Web.
• Plants and phytoplankton also emit carbon dioxide via respiration, a sort of breathing process that occurs day and night. This adds to the greenhouse effect and thus helps to warm the planet. However, they emit much less CO2 when they respire than they absorb during photosynthesis.
• Farm animals such as cattle and sheep produce the greenhouse gas methane – in their stomachs, thanks to the action of microorganisms known as methanogens – a process known as methanogenesis. The gas is emitted when these animals pass wind.
• Methanogens are also found in natural wetlands and rice paddies, both of which are major sources of methane gas. For more on this sunject, see: Why are Methane Levels Rising?
• Trees and plants emit carbon dioxide when burned. So wildfires of forest or peat typically release huge quantities of greenhouse gas into the atmosphere. In the past, these emissions would be balanced by CO2 absorption during forest regrowth, but at present rising temperatures are causing tinderbox conditions in the Arctic taiga and elsewhere, that show little sign of abating.
• Reef-building corals, crustaceans and other marine organisms that make shells and skeletons from calcium carbonate – a process known as calcification – help to lock up carbon dioxide and so exert a long term cooling effect.
What External Forcings Influence The Climate System?
The only important external climate forcing that impacts on Earth’s climate system is human-induced greenhouse gas emissions, amplified by human-induced land use change. That’s according to the Intergovernmental Panel on Climate Change (IPCC) who stated in 2013: “It is extremely likely (95 percent confidence) that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together.” 17
To be specific, the IPCC’s best estimate is that, since 1951, anthropogenic greenhouse gases have resulted in roughly 0.9°C warming, partially offset by about 0.3°C cooling from anthropogenic human aerosol emissions. During this period, natural external factors had no net influence on global temperatures. Solar activity, for instance, has been flat since 1950. 18
How Does The Climate System Deal With External Forcings?
Historically, the climate system has responded to external climate forcings in a variety of ways.
- Through an increase in the amount of outgoing radiation, following the Stefan-Boltzmann law, which lays down that as Earth’s temperature increases, the emission of infrared radiation back into space will also increase. 19 However, while this stabilizes the rise in global temperature, it does nothing about the temperature increase already experienced.
- Through increased photosynthesis by plants to remove CO2 from the atmosphere.
- Through an increase in cloud formation and a rise in evaporation. More clouds reflect more sunlight back into space.
- Through the emission of aerosols from volcanic eruption to reflect sunlight back into space.
- Through mountain uplift (e.g. of the Himalayas) in order to remove atmospheric CO2 through chemical weathering.
Can The Climate Cope With Man-Made Global Warming?
No. Despite the claims of the climate change denial machine that there is no global warming, all indicators suggest that today’s man-made climate crisis is worsening and intensifying. In addition, scientists are becoming more aware of an increasing number of interconnected climate tipping points and feedbacks, that add to the warming process, and threaten to overwhelm Earth’s climate system.
As a result, some experts are warning that our climate plan can’t cope.
- Polar glaciers are melting in Greenland and Antarctica.
- Arctic sea ice has reached record lows.
- Permafrost is thawing across the Northern Hemisphere.
- Sea levels are rising more rapidly than ever.
- The past 5 years (2014-2018) have been the five warmest years on record, and the 20 warmest years have all occurred during the past 22 years.
- Wildfires across the Arctic Circle, the Amazon Basin, Australia and California have reached record levels. During the devastating Australian bushfires 2019/2020, an estimated 1 billion animals perished, including 25,000 koala bears.
- Global energy consumption is at a record level, as are greenhouse gas emissions.
- Animal habitats are shrinking and moving, causing a serious loss of biodiversity.
- Marine ecosystems are under huge pressure from warming, acidification, deoxygenation and coral bleaching, as well as pollution from heavy metal and plastic pollutants.
- Less than one quarter of electricity comes from renewable energy sources.
For some fascinating facts about the timeline of our planet and the role of humans in its evolution, see: History of Earth in One Year (Cosmic Calendar).
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