Wednesday, April 24, 2013

Earth's Current Warmth Not Seen in the Last 1,400 Years or More, Says Study

 Apr. 21, 2013 — Fueled by industrial greenhouse gas emissions, Earth's climate warmed more between Nature Geoscience by more than 80 scientists from 24 nations analyzing climate data from tree rings, pollen, cave formations, ice cores, lake and ocean sediments, and historical records from around the world.
1971 and 2000 than during any other three-decade interval in the last 1,400 years, according to new regional temperature reconstructions covering all seven continents. This period of humanmade global warming, which continues today, reversed a natural cooling trend that lasted several hundred years, according to results published in the journal

"This paper tells us what we already knew, except in a better, more comprehensive fashion," said study co-author Edward Cook, a tree-ring scientist at Lamont-Doherty Earth Observatory who led the Asia reconstruction.

The study also found that Europe's 2003 heat wave and drought, which killed an estimated 70,000 people, happened during Europe's hottest summer of the last 2,000 years. "Summer temperatures were intense that year and accompanied by a lack of rain and very dry soil conditions over much of Europe," said study co-author Jason Smerdon, a climate scientist at Lamont-Doherty and one of the lead contributors to the Europe reconstruction. Though summer 2003 set a record for Europe, global warming was only one of the factors that contributed to the temperature conditions that summer, he said.

The study is the latest to show that the Medieval Warm Period, from about 950 to 1250, may not have been global, and may not have happened at the same time in places that did grow warmer. While parts of Europe and North America were fairly warm between 950 and 1250, South America stayed relatively cold, the study says. Some people have argued that the natural warming that occurred during the medieval ages is happening today, and that humans are not responsible for modern day global warming. Scientists are nearly unanimous in their disagreement "If we went into another Medieval Warm Period again that extra warmth would be added on top of warming from greenhouse gases," said Cook.

Temperatures varied less between continents in the same hemisphere than between hemispheres. "Distinctive periods, such as the Medieval Warm Period or the Little Ice Age stand out, but do not show a globally uniform pattern," said co-author Heinz Wanner, a scientist at the University of Bern. By 1500, temperatures dropped below the long-term average everywhere, though colder temperatures emerged several decades earlier in the Arctic, Europe and Asia.

The most consistent trend across all regions in the last 2,000 years was a long-term cooling, likely caused by a rise in volcanic activity, decrease in solar irradiance, changes in land-surface vegetation, and slow variations in Earth's orbit. With the exception of Antarctica, cooling tapered off at the end of the 19th century, with the onset of industrialization. Cooler 30-year periods between 830 and 1910 were particularly pronounced during weak solar activity and strong tropical volcanic eruptions. Both phenomena often occurred simultaneously and led to a drop in the average temperature during five distinct 30- to 90-year intervals between 1251 and 1820. Warming in the 20th century was on average twice as large in the northern continents as it was in the Southern Hemisphere. During the past 2000 years, some regions experienced warmer 30-year intervals than during the late 20th century. For example, in Europe the years between 21 and 80 AD were likely warmer than the period 1971-2000.

Tuesday, April 9, 2013

Air pollution stunts coral growth

Air pollution stunts coral growth

Apr. 7, 2013 — A new study has found that pollution from fine particles in the air -- mainly the result of burning coal or volcanic eruptions -- can shade corals from sunlight and cool the surrounding water resulting in reduced growth rates.

Although coral reefs grow under the sea it seems that they have been responding to changes in the concentration of particulate pollution in the atmosphere, according to a paper published in the journal Nature Geoscience bya team of climate scientists and coral ecologists from the UK, Australia and Panama. Corals are colonies of simple animal cells but most rely on photosynthetic algae for their energy and nutrients.
Lead author Lester Kwiatkowski, a PhD student from Mathematics at the University of Exeter, said: "Coral reefs are the most diverse of all ocean ecosystems with up to 25% of ocean species depending on them for food and shelter. They are believed to be vulnerable to climate change and ocean acidification, but ours is the first study to show a clear link between coral growth and the concentration of particulate pollution in the atmosphere."
Dr Paul Halloran of the Met Office Hadley Centre explained: "Particulate pollution or 'aerosols' reflect incoming sunlight and make clouds brighter. This can reduce the light available for coral photosynthesis, as well as the temperature of surrounding waters. Together these factors are shown to slow down coral growth."
he authors used a combination of records retrieved from within the coral skeletons, observations from ships, climate model simulations and statistical modelling. Their analysis shows that coral growth rates in the Caribbean were affected by volcanic aerosol emissions in the early 20th century and by aerosol emissions caused by humans in the later 20th century.
The researchers hope that this work will lead to a better understanding of how coral growth may change in the future, taking into account not just future carbon dioxide levels, but also localised sources of aerosols such as industry or farming.
Professor Peter Mumby of the University of Queensland put the study in the context of global environmental change: "Our study suggests that coral ecosystems are likely to be sensitive to not only the future global atmospheric carbon dioxide concentration but also the regional aerosol emissions associated with industrialisation and decarbonisation."
The study was financially supported by a NERC grant, the University of Exeter and the EU FORCE project.
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