Evidence from the last warm period in the Earth's ancient past suggests the climate will respond as expected to rising CO2 levels.
The research, published in Nature, is in line with future predictions from the IPCC, says the UK-led team.
The evidence came from ancient plankton fossils drilled from the ocean floor.
These creatures' shells contain clues as to how the global climate cycled from cool to warm many times some 2.3 to 3.3 million years ago, across what researchers refer to as the Pliocene and Pleistocene Epochs in Earth history.
Scientists from the UK and Australia used this ancient climate record to reconstruct the CO2 content of the planet's atmosphere, comparing it to a separate record of CO2 acquired from bubbles of ancient atmosphere trapped in ice drilled from the poles.
"We have shown that the change in Earth's temperature for a given change in CO2, once the effect of the growth and retreat of the highly reflective continental ice sheets was taken into account, was not only identical during both the cold Pleistocene and warm Pliocene periods, but was also similar to the understanding recently summarised by the Intergovernmental Panel on Climate Change (IPCC)," said co-researcher Dr Gavin Foster of the University of Southampton.
"This implies that as we approach a Pliocene-like future, the IPCC range of climate sensitivity is likely to be suitable for describing the degree of warming we should expect."
Read more at Ancient Climate Records 'Back Predictions'
This study is based upon the analysis of seabed sediments which were transported by icebergs around 2.2 to 4.3 million years ago, and which have been collected during an expedition by the Integrated Ocean Drilling Program.
The data obtained reveal that natural climatic processes can increase the response of polar ice caps to minor changes in energy caused by modifications in earth's orbit. The sea level can either decrease or increase by as much as dozens of meters. This study shows that 2.5 million years ago, when the concentration of carbon dioxide in the atmosphere was similar to the current one, the thawing of the eastern Antarctic ice cap was a generalized process.
"This study helps solve the mystery of how the Earth's orbit around the Sun contributes to the stability of ice caps," according to Carlota Escutia, a researcher at the Andalusian Institute of Earth Sciences (a CSIC-UGR joint institution), which has led the expedition.
Greenhouse effect gases
"The emission of greenhouse effect gases has, nevertheless, a much larger energy impact than that provided by any changes in the earth's orbit," according to Escutia.
The analysis of sediments shows that the stability of the largest ice cap on earth is influenced by the presence of sea ice in the oceans that surround Antarctica. This sea ice is a layer of frozen seawater that creates a protective shield around the continent and the Antarctic ice caps, and it is sensitive to the warming up of oceans generated as a result of the increase in greenhouse effect gasses. "The disappearance of this sea ice can result in the melting of the ice caps and in the increase of sea level by several meters," adds Escutia.
Millions of years ago, under conditions of high concentration of carbon dioxide -- as is also the case now -- and ocean temperatures slightly higher than those currently registered, the oceans surrounding Antarctica could no longer sustain the sea ice. Escutia points out that "the disappearance of this protective shield allowed oceanic currents pushed by the winds to penetrate down to the base of the ice caps, provoking their thaw."
This study speculates with a potentially generalized thaw of Antarctica's Eastern ice cap in the future if we fail to reduce the levels of carbon dioxide in the atmosphere.
Read more at Earth's Orbit Affects the Stability of Antarctica's Eastern Ice Cap
Many marine organisms--such as coral, clams, mussels, sea urchins, barnacles, and certain microscopic plankton--rely on equilibrated chemical conditions and pH levels in the ocean to build their calcium-based shells and other structures. A new analysis published in the journal Environmental Science and Technology provides a holistic analysis of how species will be affected worldwide under different climate scenarios.
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"Previous studies have shown that marine species were being negatively affected by decreasing ocean pH levels. But until now most studies looked at individual species. This study is one of the first to analyze the impact on the whole community of calcifying species, while also looking at both pH levels and CO2 partial pressure," says Azevedo.
The study examines the impact of increased ocean acidity on species growth, reproduction, and survival. It used two climate change scenarios from the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5): in the low emissions scenario, ocean pH is projected to decrease from 8.1 to 7.95, while in the high emissions scenario, median ocean pH is expected to decrease to 7.80. (Lower pH indicates higher acidity).
The analysis finds that under the high emissions scenario, between 21-32% of calcifying species would be significantly affected, based on a threshold of 10% of a species population being affected. In the low emissions scenario, only 7-12% of species would be affected.
Azevedo notes that while the study is an important new milestone for ocean acidification research, it does not show what level of impact which species population can handle, that is, how much acidification is too much.
"It's hard to say what the level of impact would mean for different organisms -- a 10% rate could be no problem for some species, but for other more sensitive species it could mean one step closer to local extinction," explains Azevedo.
Read more at How Will Ocean Acidification Impact Marine Life?
Skeptics who still doubt anthropogenic climate change have now been stripped of one of their last-ditch arguments: it is true that there has been a warming hiatus and that the surface of Earth has warmed up much less rapidly since the turn of the millennium than all the relevant climate models had predicted. However, the gap between the calculated and measured warming is not due to systematic errors of the models, as the skeptics had suspected, but because there are always random fluctuations in Earth's climate, according to a comprehensive statistical analysis.
Read more at Global Warming Slowdown: No Systematic Errors in Climate Models, Comprehensive Statistical Analysis Reveals
![Forecasts without systematic errors: climate models, such as the model MPI - ESM LR of the Max Planck Institute for Meteorology, predict a significant increase in temperature by the end of this century, especially at the Earth's poles. No model, however, has predicted the global warming hiatus which climate researchers have observed since the turn of the millennium. This, however, is not due to systematic errors of the models, but to random fluctuations in the climate system. The model predictions are therefore reliable, taking some statistical uncertainty into account. (Credit: MPI for Meteorology / Deutsches Klimarechenzentrum [DKRZ]) Click to Enlarge.](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLKdxyaVhv9pDZGZEF0mwCknXlfcQRZxE3IKWCI8tFUj4A80zdtJD3bXN7XigImGieg1qIhNu2UBcZdFeJITKyD9upbjk0uMtHXPll33BFyeb38Amhvm9IAE-fdGK3hOh9luHQFFS_bd6G/s1600/150202114636-large.jpg "Forecasts without systematic errors: climate models, such as the model MPI - ESM LR of the Max Planck Institute for Meteorology, predict a significant increase in temperature by the end of this century, especially at the Earth's poles. No model, however, has predicted the global warming hiatus which climate researchers have observed since the turn of the millennium. This, however, is not due to systematic errors of the models, but to random fluctuations in the climate system. The model predictions are therefore reliable, taking some statistical uncertainty into account. (Credit: MPI for Meteorology / Deutsches Klimarechenzentrum [DKRZ]) Click to Enlarge.")