Page 369 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 11 Climate Change 333
natural gas reserves combined. These deposits occur at depths greater than about 900 m under seafloor sediments. Several countries are exploring the use of methane hydrates as an energy source. in March 2013, Japan’s deep-water ocean drilling rig, Chikyu, successfully extracted gas hydrates from a depth of 1000 m in the Pacific Ocean. The coun- try’s goal is to achieve commercial production of methane hydrates within 6 years. However, the pos- sibility of accidental uncontrolled methane releases during extrac- tion is an important concern.
Under today’s conditions of atmospheric warming, scientists
think that the thawing of methane hydrates from two of its general
source regions can potentially
affect atmospheric methane concentrations (Figure 11.1.2).
On land, at high latitudes in the
arctic, permafrost could thaw to
depths of 180 m, causing meth-
ane hydrates in rock to dissociate. in the arctic Ocean, below subsea permafrost at shallow depths along continental shelves, rising ocean and land temperatures could also thaw permafrost to depths that would compromise hydrate structures. in the east Siberian Sea, off the shore of northern russia, scientists think that an estimated 45 billion tonnes of methane stored in
the form of hydrates is already beginning to dissociate, producing rising plumes
Shoreline
Warmed ocean
Continental shelf
Methane bubbles
Thawing permafrost
Escape vents
Methane hydrates
Thawing tundra Deep lake
On land, thawing permafrost can extend downward until it reaches gas hydrates.
In the ocean, warming water can thaw shallow permafrost, melting the hydrates below.
▲Figure 11.1.2 Methane hydrate deposits in arctic permafrost and under continental shelves. Two theoretical pathways for methane hydrate thaw: On land, thawing permafrost can extend downward until it reaches gas hydrates; in the ocean, warming water can thaw shallow permafrost, melting the hydrates below. [Based on Walter anthony, k. 2009. Methane: a menace surfaces. Scientific American 301: 68–75 doi:10.1038/scientificamerican1209-68.]
of methane that reach the atmosphere. The process, they think, is triggered by changes in summer sea ice, whose extent has declined so much above the Siberian shelf that ocean surface temperatures
in ice-free areas have warmed as much
as 7 C°, according to satellite data. The warming extends downward about 50 m to the shallow seafloor, melting the frozen sediments. in areas where the seabed
is deeper along continental slopes, gas hydrates may dissociate if ocean warming
continues, but scientists do not yet know whether the methane released would reach the atmosphere.
The overall processes and environ- mental effects of methane hydrate thaw are a focus of ongoing research. For more information, see the article “good gas, Bad gas” at ngm.nationalgeographic .com/2012/12/methane/lavelle-text and the U.S. geological Survey gas Hydrates Project page at woodshole.er.usgs.gov/ project-pages/hydrates/.
Scientific Consensus
The world’s climate scientists have reached overwhelm- ing consensus that human activities are causing climate change, agreement that is confirmed throughout the sci- entific community. Several recent surveys illustrate this consensus; for example, a 2009 survey published in the Proceedings of the National Academy of Sciences found
that 97%–98% of actively publishing climate scientists support the conclusion that ongoing climate change is an- thropogenic.* Numerous policy statements and position
*See “William R. L. Anderegg et al., “Expert Credibility on Climate Change,” Proceedings of the National Academy of Sci- ences, early ed., 2009. (Available at www.pnas.org/content/early/ 2010/06/04/1003187107.)
Georeport 11.3 Causes of Extreme Weather Events in a Changing Climate
according to the 2013 nOaa report “explaining extreme events of 2012 from a Climatic Perspective,” Bulletin of the American Meteorological Society, Volume 94 (9), scientific analyses of 12 extreme weather and climate events in 2012 found
that anthropogenic climate change was a contributing factor to half the events—either to their occurrence or outcomes—and that the magnitude and likelihood of each were boosted by climate change. also important for these extreme events was the role of natural climate and weather fluctuations, such as el niño–Southern Oscillation and other global circulation patterns, factors that may be af- fected by global warming. The new, developing science of “event attribution” seeks to find the causes of extreme weather and climate events and has important applications for risk management, prepartion for future events, and overall mitigation of climate change effects. in 2014, nOaa updated and expanded this report, available at www.ncdc.noaa.gov/news/explaining-extreme-events-2013.