Climate variability and change

Such changes can be the result of "internal variability", when natural processes inherent to the various parts of the climate system alter the distribution of energy.

Climate variability has consequences for sea level changes, plant life, and mass extinctions; it also affects human societies.

External forcing can be either anthropogenic (e.g. increased emissions of greenhouse gases and dust) or natural (e.g., changes in solar output, the Earth's orbit, volcano eruptions).

A combination is also possible, e.g., sudden loss of albedo in the Arctic Ocean as sea ice melts, followed by more gradual thermal expansion of the water.

Due to climate inertia, this signal can be 'stored' in the ocean and be expressed as variability on longer time scales than the original weather disturbances.

The ocean and atmosphere can work together to spontaneously generate internal climate variability that can persist for years to decades at a time.

[36] Life affects climate through its role in the carbon and water cycles and through such mechanisms as albedo, evapotranspiration, cloud formation, and weathering.

[54] The US Geological Survey estimates are that volcanic emissions are at a much lower level than the effects of current human activities, which generate 100–300 times the amount of carbon dioxide emitted by volcanoes.

However, there is evidence for the presence of water on the early Earth, in the Hadean[66][67] and Archean[68][66] eons, leading to what is known as the faint young Sun paradox.

[69] Hypothesized solutions to this paradox include a vastly different atmosphere, with much higher concentrations of greenhouse gases than currently exist.

[72] This is due to the optical properties of SO2 and sulfate aerosols, which strongly absorb or scatter solar radiation, creating a global layer of sulfuric acid haze.

[78] [79] Small eruptions, with injections of less than 0.1 Mt of sulfur dioxide into the stratosphere, affect the atmosphere only subtly, as temperature changes are comparable with natural variability.

[72][80] Over the course of millions of years, the motion of tectonic plates reconfigures global land and ocean areas and generates topography.

[82][83] During the Carboniferous period, about 300 to 360 million years ago, plate tectonics may have triggered large-scale storage of carbon and increased glaciation.

To test the hypothesis, CERN designed the CLOUD experiment, which showed the effect of cosmic rays is too weak to influence climate noticeably.

[86][87] Evidence exists that the Chicxulub asteroid impact some 66 million years ago had severely affected the Earth's climate.

It uses a variety of proxy methods from the Earth and life sciences to obtain data preserved within things such as rocks, sediments, ice sheets, tree rings, corals, shells, and microfossils.

The primary sources include written records such as sagas, chronicles, maps and local history literature as well as pictorial representations such as paintings, drawings and even rock art.

Quantification of climatological variation of precipitation in prior centuries and epochs is less complete but approximated using proxies such as marine sediments, ice cores, cave stalagmites, and tree rings.

The study of these ice cores has been a significant indicator of the changes in CO2 over many millennia, and continues to provide valuable information about the differences between ancient and modern atmospheric conditions.

Climate change devastated these tropical rainforests, abruptly fragmenting the habitat into isolated 'islands' and causing the extinction of many plant and animal species.

[112] Collapses of past civilizations such as the Maya may be related to cycles of precipitation, especially drought, that in this example also correlates to the Western Hemisphere Warm Pool.

Around 70 000 years ago the Toba supervolcano eruption created an especially cold period during the ice age, leading to a possible genetic bottleneck in human populations.

The most significant climate processes since the middle to late Pliocene (approximately 3 million years ago) are the glacial and interglacial cycles.

[114] Shaped by orbital variations, responses such as the rise and fall of continental ice sheets and significant sea-level changes helped create the climate.

[119] When there is a lot of sea ice present globally, especially in the tropics and subtropics, the climate is more sensitive to forcings as the ice–albedo feedback is very strong.

[123] The PETM represents a "case study" for modern climate change as in the greenhouse gases were released in a geologically relatively short amount of time.

[102] In contrast, the world's climate was cloudier and wetter than today near the start of the warm Atlantic Period of 8000 years ago.

Shifts in biomes and habitat ranges are also unprecedented, occurring at rates that do not coincide with known climate oscillations [citation needed].

The decline in Arctic sea ice, both in extent and thickness, over the last several decades is further evidence for rapid climate change.

There is seasonal variability in how new high temperature records have outpaced new low temperature records. [ 11 ]
Colored bars show how El Niño years (red, regional warming) and La Niña years (blue, regional cooling) relate to overall global warming . The El Niño–Southern Oscillation has been linked to variability in longer-term global average temperature increase.
A schematic of modern thermohaline circulation . Tens of millions of years ago, continental-plate movement formed a land-free gap around Antarctica, allowing the formation of the ACC , which keeps warm waters away from Antarctica.
CO 2 concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black)
Milankovitch cycles from 800,000 years ago in the past to 800,000 years in the future.
Variations in solar activity during the last several centuries based on observations of sunspots and beryllium isotopes. The period of extraordinarily few sunspots in the late 17th century was the Maunder minimum .
In atmospheric temperature from 1979 to 2010, determined by MSU NASA satellites, effects appear from aerosols released by major volcanic eruptions ( El Chichón and Pinatubo ). El Niño is a separate event, from ocean variability.
Variations in CO 2 , temperature and dust from the Vostok ice core over the last 450,000 years.
Top: Arid ice age climate
Middle: Atlantic Period , warm and wet
Bottom: Potential vegetation in climate now if not for human effects like agriculture. [ 102 ]
Climate changes over the past 65 million years, using proxy data including Oxygen-18 ratios from foraminifera .
Temperature change over the past 12 000 years, from various sources. The thick black curve is an average.
Global warming has varied substantially by latitude, with the northernmost latitude zones experiencing the largest temperature increases.