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気になった一文集(English ver. No. 22)

The Northern Hemisphere jet stream flows from west to east at mid-latitudes; it deviates from a line of latitude through a series of ripples called Rossby waves. Regions above which the jet stream is flowing from the north are likely to experience cold weather. Conversely, in regions above which it flows from the south, the weather is likely to be relatively warm. The larger the amplitude of the Rossby waves, the more anomalous the weather is likely to be at the surface.

Anomalous latent heat release in the tropical West Pacific can produce a particularly strong Rossby wave response in the Northern Hemisphere. The phase of this Rossby wave response is consistent with the cold and snowy season seen in the U.S. Midwest and East Coast. If this line of argument is correct, the extremely cold and snowy season in parts of the United States may indeed have been caused at least in part by increased greenhouse gas concentrations.

Earth's climate is a complex system, and its response to some external forcing will not be linear. Because of this complexity, sophisticated climate models are needed to test the correctness and robustness of climate mechanisms. Running these models is computationally expensive but crucial for advancing understanding of current and future climate.

Current seasonal forecast models suggest that a new (warm) phase of the El Niño/Southern Oscillation phenomenon may begin later this year, when the trade winds will finally weaken. If an El Niño event is on the way, the hiatus period may be coming to a close. If so, the upside is that the residents of the U.S. Midwest will be much less likely to have to suffer very cold winters. The downside is that global temperatures are likely to start to rise again, with many undesirable consequences for humans across the planet. The only way to reduce the risks associated with man-made climate change, in Detroit or elsewhere, is to cut greenhouse gas emissions.

Record-breaking winters and global climate changeScience 344, 803-804 “PERSPECTIVE


Of the roughly 10 billion tonnes of carbon emitted each year from human activity, only around half remains in the atmosphere, with the rest being absorbed by the oceans and by plants on land. This CO2 sink has been growing steadily, but the situation could change as shifts in climate and human land use intensify.

Their results challenge the current consensus about what regulates atmospheric CO2 from year to year, and will prove invaluable as societies struggle to predict, and adapt to, changes in a world in which both atmospheric and ecological systems are moving into unfamiliar territory.

A switch in the type of ecosystem that controls atmospheric CO2 has major implications for the overall rate and pattern of climate change. First, different vegetation types may have different responses and sensitivities to disturbance. For example, Poulter et al. show that increased growth of vegetation in semi-arid ecosystems is linked not only to generally increasing levels of rainfall across these regions, but also to increasing sensitivity of the vegetation to rainfall. (…) Second, different types of ecosystem lock away absorbed CO2 for different lengths of time. Rainforests store much of their carbon in dense hardwoods, which may take many centuries to die and rot, whereas much of the CO2 absorbed across semi-arid regions is converted into relatively short-lived grasses and shrubs.

Although Poulter and colleagues use the best available models to support their conclusions, models are only as good as the data with which they are calibrated, and little information exists about vegetation in semi-arid ecosystems compared with other regions. Similarly, the pathways for CO2 once it has been absorbed into semi-arid vegetation remain poorly understood, so there are few solid data from which to assess the stability of the CO2 sink in such ecosystems.

Nevertheless, Poulter et al. make a key contribution in highlighting the crucial, and hitherto often overlooked, role of such ecosystems in the global carbon cycle, and in identifying several important processes, which should markedly improve our understanding of future atmospheric CO2 levels. Let us hope that their research stimulates more work on the ground to better understand and manage these fragile but essential ecosystems.

A sink down underNature 509, 566–567 (29 May 2014). “NEWS & VIEWS


Continuing uncertainty fuels the argument of those sceptical of global warming, that society should avoid acting on such ‘shaky’ science. Given that massive decarbonization could have major economic implications, this argument can seem compelling. But to ‘wait and see’ could trigger hugely dangerous impacts if temperatures increase to the higher end of predicted ranges. 

Thermal lags could create false optimism, as a CO2 concentration unrecognized as dangerous may be reached a few decades before the full temperature implications are realized. Then, even if mitigation measures somehow reduced net CO2 emissions to near zero, the planet would take centuries to reset itself. Forewarned is forearmed when preparing for climate change.

Refining global warming projectionsNature Climate Change 3, 704–705 (2013)


For either conventional CCS or BECCS, the cost must come down. Right now, CCS costs range from about $30 to $140 per ton of CO2, depending on the source from which it is captured, the capture technology, and the form of storage.

Capturing and storing 1 Gt of CO2 from the atmosphere using BECCS would require about 0.5 to 1 Gt of biomass (equivalent to 10 to 20 exajoules of primary energy). Concerns about whether this much biomass could be practically and sustainably harvested, dried, and collected at this scale without interfering with food production or negatively affecting other ecosystem services must be examined.

Negative-emissions technologies such as BECCS can be thought of as part of an insurance policy for climate change mitigation. This approach still leaves unanswered questions, but to not consider it carefully would be too risky.

Negative-emissions insuranceScience 344, 1431 (27 June 2014) "Editorial"


Australia’s decision highlights the crude reality that political decision-making does not necessarily follow the logics of science and economics.

Australia, one of the world’s richest countries and a leading per capita carbon emitter, must do more to reassure the rest of the world that it is ready to join global efforts to tackle climate change. If it does not, it would send a devastating signal to rising economies such as China that will play a key part in negotiations leading up to an inter­national climate agreement. These nations must be involved in global climate action, but they will hardly be persuaded to sign up if an industrial power the size of Australia falters.

The wrong kind of carbon cutNature 511, 383 (22 July 2014) “Editorial


Emissions from the Australian energy sector fell by 5% after the introduction of a carbon tax.

Australia’s total greenhouse-gas emissions — 538.4 million tonnes of CO2 equivalent in 2013, down 0.8% from 2012 — account for less than 1.5% of total global emissions. But owing to extensive use of coal in electricity generation, the country is one of the world’s largest polluters on a per capita basis.

…Australia’s U-turns on the carbon tax and other climate policies may discourage other nations from being as ambitious as they might have been, says Elliot Diringer.
”オーストラリアの炭素税とその他気候政策におけるUターンは、他の国家がこれまでのように(気候政策に対して)野心的であったことのやる気を失わせるかもしれない”と、Elliot Diringerは言う。

“The government’s relatively weak and ineffective action on climate change is not consistent with a fair contribution from Australia towards global efforts to avoid dangerous climate change,” says David Karoly.
”気候変化に対するオーストラリア政府の比較的弱い、非効果的な行動は、危険な気候変化を回避するための世界的な努力に対してオーストラリアが行っている寄与に見合わない”と、David Karolyは言う。

Economists think that carbon pricing is the most efficient way to cut emissions. But Michael Grubb, who studies energy and climate policies at University College London, says that this often ignores the political reality — where decision-making tends to follow voters’ immediate wishes and concerns.
経済学者は炭素価格はCO2排出を削減するのにもっとも効果的であると考えている。しかしユニヴァーシティ・カレッジ・ロンドンでエネルギー・気候政策を研究するMichael Grubbは、”それは政治における、「意思決定が投票者のつかの間の望みと関心に従う傾向がある」という真実をしばしば無視している”と言う。

Anger as Australia dumps carbon taxNature 511, 392 (24 July 2014) “Nature NEWS