Extreme weather, made by us?

September 2015 - via Science Journal Anthropogenic climate change is expected to increase the frequency of heat waves and other extreme weather events (1). When such an event occurs, it is natural to ask whether it can be attributed to human activities. Conventional wisdom has long held that although it is possible to attribute an increase in the frequency of extreme events to human activities, the same is not true of individual events. Recent studies that appear to identify the role of anthropogenic climate change in, among other events, the 2010 Russian heat wave (2), the 2013 Australian heat wave (3), and the ongoing drought in California (see the photo) (4) suggest that this conventional wisdom has been overturned. But has it? Read more: Extreme weather, made by us?

Oceanic sink changes

September 2015 - via Science Journal The North Atlantic is one of the world's most important ocean carbon sinks, which partly mitigate climate change. However the efficiency of CO2 uptake is expected to be reduced by changes in circulation and biological processes, although the magnitude of their effect is unclear. Read more: Oceanic sink changes

The reinvigoration of the Southern Ocean carbon sink

September 2015 - via Science Journal Several studies have suggested that the carbon sink in the Southern Ocean—the ocean’s strongest region for the uptake of anthropogenic CO2 —has weakened in recent decades. We demonstrated, on the basis of multidecadal analyses of surface ocean CO2observations, that this weakening trend stopped around 2002, and by 2012, the Southern Ocean had regained its expected strength based on the growth of atmospheric CO2. All three Southern Ocean sectors have contributed to this reinvigoration of the carbon sink, yet differences in the processes between sectors exist, related to a tendency toward a zonally more asymmetric atmospheric circulation. The large decadal variations in the Southern Ocean carbon sink suggest a rather dynamic ocean carbon cycle that varies more in time than previously recognized. Read more: The reinvigoration of the Southern Ocean carbon sink

An increasing carbon sink?

September 2015 - via Science Journal Since 1870, Earth's oceans have absorbed more than one-quarter of the carbon dioxide emitted to the atmosphere from fossil fuel burning and other human activities, thereby dramatically slowing climate change (1). The Southern Ocean is responsible for ~40% of this global ocean carbon sink (2). Recent studies have suggested that the rate of carbon uptake by the Southern Ocean may be slowing (3, 4). Such a positive climate feedback effect would reduce the Southern Ocean's capacity to slow climate change. On page 1221 of this issue, Landschützer et al. show that although the rate of carbon uptake by the Southern Ocean slowed between the 1980s and early 2000s, it began to strengthen again in 2002 and continued to do so until at least 2012 (5). Read more: An increasing carbon sink?

Meteorology: Big coastal storms to come

September 2015 - via Nature Journal Three major coastal cities on different continents could get walloped by tropical cyclones during the next century because of climate change. Ning Lin of Princeton University in New Jersey and Kerry Emanuel of the Massachusetts Institute of Technology in Cambridge ran statistical models of how storms form near the cities of… Read more: Big coastal storms to come

Carbon dioxide levels peak up high

August 2015 - via Nature Journal The carbon dioxide concentration in Earth's upper atmosphere is increasing at more than twice the average rate observed at the surface. Jia Yue of Hampton University in Virginia and his colleagues analysed CO2 measurements at different atmospheric heights and latitudes between 2002 and 2014 using a satellite-borne infrared radiometer. They found… Read more: Carbon dioxide levels peak up high

Soil carbon trends

August 2015 - via Nature Climate Change Soils contain the largest carbon stock in the terrestrial biosphere, so their response to climate change is important. However, soil carbon responses to warming from both modelling and experimental studies are mixed, and the net effect remains unclear. Read more: Soil carbon trends

Temperate forest health in an era of emerging megadisturbance

August 2015 - via Science Journal Although disturbances such as fire and native insects can contribute to natural dynamics of forest health, exceptional droughts, directly and in combination with other disturbance factors, are pushing some temperate forests beyond thresholds of sustainability. Interactions from increasing temperatures, drought, native insects and pathogens, and uncharacteristically severe wildfire are resulting in forest mortality beyond the levels of 20th-century experience. Additional anthropogenic stressors, such as atmospheric pollution and invasive species, further weaken trees in some regions. Although continuing climate change will likely drive many areas of temperate forest toward large-scale transformations, management actions can help ease transitions and minimize losses of socially valued ecosystem services. Read more here: Temperate forest health in an era of emerging megadisturbance

Beef farming brings on warming

August 2015 - via Science Journal The most climate-friendly methods of beef production may not be enough to reduce the environmental effects of raising cattle. Mark Newman/FLPA/imagebroker/REX Raymond Pierrehumbert at the University of Oxford, UK, and Gidon Eshel at Bard College in Annandale-on-Hudson in New York modelled the warming effects of five different ways of producing beef, including intensive feedlot systems (pictured) and pasture-based methods. Their analysis was based on the known amounts of greenhouse gases produced by each method. Read more: Beef farming brings on warming

Drought effects on carbon cycling

July 2015 - via Science Journal The impacts of climate extremes on terrestrial ecosystems are poorly understood but important for predicting carbon cycle feedbacks to climate change. Coupled climate–carbon cycle models typically assume that vegetation recovery from extreme drought is immediate and complete, which conflicts with the understanding of basic plant physiology. We examined the recovery of stem growth in trees after severe drought at 1338 forest sites across the globe, comprising 49,339 site-years, and compared the results with simulated recovery in climate-vegetation models. We found pervasive and substantial “legacy effects” of reduced growth and incomplete recovery for 1 to 4 years after severe drought. Legacy effects were most prevalent in dry ecosystems, among Pinaceae, and among species with low hydraulic safety margins. In contrast, limited or no legacy effects after drought were simulated by current climate-vegetation models. Our results highlight hysteresis in ecosystem-level carbon cycling and delayed recovery from climate extremes. Read more: Pervasive drought legacies in forest ecosystems and their implications for carbon cycle models

Recent hiatus caused by decadal shift in Indo-Pacific heating

July 2015 - by Veronica Nieves, Josh K. Willis, William C. Patzert - via Science Journal Recent modeling studies have proposed different scenarios to explain the slowdown in surface temperature warming in the most recent decade. Some of these studies seem to support the idea of internal variability and/or rearrangement of heat between the surface and the ocean interior. Others suggest that radiative forcing might also play a role. Our examination of observational data over the past two decades shows some significant differences when compared to model results from reanalyses and provides the most definitive explanation of how the heat was redistributed. We find that cooling in the top 100-meter layer of the Pacific Ocean was mainly compensated for by warming in the 100- to 300-meter layer of the Indian and Pacific Oceans in the past decade since 2003. Read more: Recent hiatus caused by decadal shift in Indo-Pacific heating

Sea warming caused extreme rain (Russia 2012)

July 2015 - via Nature Journal Intense rainfall that caused a devastating flash flood in a Russian town in 2012 (pictured) has been linked to the increasing surface temperature of the Black Sea. Mikhail Mordasov/AFP/Getty The flood in the town of Krymsk killed more than 170 people after an unprecedented amount of rain — twice the previous record — fell in a single night. Edmund Meredith at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, and his co-workers used an atmospheric model to study the sensitivity of this event to Black Sea warming. They found that simulations using current Black Sea surface tem… Read more: Black Sea warming caused extreme rain