Aaron Bernstein, Associate Director of the Center for Health and the Global Environment, Boston Children’s Hospital, Harvard:

Much research has shown that warming and elevated \(CO_2\) have made pollen seasons longer and pollen more abundant. See eg http://nca2014.globalchange.gov/highlights/report-findings/human-health/graphics/ragweed-pollen-season-lengthens

Aaron Bernstein, Associate Director of the Center for Health and the Global Environment, Boston Children’s Hospital, Harvard:

For starters, many experienced leaders - military, political, and otherwise, are extremely concerned about the threat climate change poses to security. See the American Security Project’s work on climate security.

In addition, growing staple crops at higher \(CO_2\) reduces their nutritional value.

While some regions have benefited from recent warming, extreme events associated with climate change have already destabilized the world food system. Models consistently show that climate change will adversely effect crop output.

The best available science also shows that even in the past few decades climate change has reduced food production, by as much as 5 billion dollars per year as of 2002.

Aaron Bernstein, Associate Director of the Center for Health and the Global Environment, Boston Children’s Hospital, Harvard:

This may be true for some areas but models have consistently shown that precipitation will be more in some places and less in others.

See for instance how rainfall have already changed: source: http://www.climatechange2013.org/

Overall scientific credibility: 'very low', according to 12 scientists who analyzed this article.

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Martin Truffer, Professor of Physics, University of Alaska Fairbanks:

The author does not know what he is referring to when he says 'the Antarctic Ice Sheet'. What has been expanding is the extent of sea ice around Antarctica, not the Antarctic Ice Sheet. While icebergs routinely break off Antarctica, the release of this particular iceberg was significant. Iceberg calving from Pine Island Glacier has been occurring at ever increasing rates, and the line of contact between the glacier and the ocean (the grounding line) keeps retreating. It looks even worse at nearby Thwaites Glacier that is now on the brink of unstable retreat, or has already crossed that threshold. See, for example:

Joughin et al (2014). Marine Ice Sheet Collapse Potentially Underway for the Thwaites Glacier Basin, West Antarctica.

The basins of Thwaites and Pine Island Glacier hold enough ice to raise global sea level by 1.5 m.

Kevin Trenberth, Senior Scientist, National Center for Atmospheric Research:

This is incorrect. While there have been some claims of increased cold outbreaks, winters are warming in general. Cooling has been episodic and very local. On the other hand, there is considerable research that understands the life cycle of these and other pests: how that can have two reproduction cycles per year instead on one, and how cold weather in winter kills them off.

Trenberth, et al 2014: Seasonal aspects of the recent pause in surface warming.

Kevin Trenberth, Senior Scientist, National Center for Atmospheric Research:

This is nonsense. Global precipitation has not changed significantly since 1979 when we first have global values. Precipitation on land benefits from La Nina or negative PDO* conditions as more rain occurs on land. From 1999 to 2013 the PDO was negative. In spite of that, drought has increased globally somewhat: see Trenberth et al 2014.

*Pacific Decadal Oscillation

Kevin Trenberth, Senior Scientist, National Center for Atmospheric Research:

This is wrong. A very nice column on this by David Karoly has recently appeared in The Conversation.

Michael Wehner, Senior Staff Scientist, Lawrence Berkeley National Laboratory:

The link is to a blog by the author mostly about tornadoes. There is no consensus about tornadoes and climate change as of yet. There is indeed a recent drought in landfalling Atlantic hurricanes, which is also not well understood.

But the falsehoods in the statement quoted above remain.

1) Hurricanes. Recent modeling efforts from multiple groups, including mine, are reaching a consensus that at the GLOBAL scale, a warmer world will experience fewer named tropical cyclones. However, there is also a shift towards more intense hurricanes (cat 4 and 5) in these warmer simulations. It is important to note that a detectible signal in tropical cyclone statistics has not emerged. And a decline in number or intensity has certainly not been either detected nor attributed to anything at the global scale.

The claim is thus false.

2) Heat waves. Nothing could be farther from the truth than this quoted statement. See this recent paper for instance: Attribution of extreme temperature changes during

This example misses the point completely about probabilistic extreme event attribution. An event attribution statement is not “Climate change caused this event” Rather, an attribution statement reads more like: “Climate change doubled the chance of this heat wave reaching the observed temperature”.

Implicit in this statement is that the probability of the heat wave in the pre-industrial world was not zero. As of this time, no event has been claimed to have been impossible prior to the human interference in the climate system. This could change in a 6K warmer world as projected in some 'business as usual' simulations.

So the bottom line is not that some heat wave in the distant past disproves climate change, rather that the odds of that event occurring again has increased. And that statement is true everywhere that has long observational records.

3) Droughts. On this matter, I am very conservative. But it is important to define what you mean by drought. Meteorological, agricultural or hydrological? Droughts usually involve all of these to some extent. Precipitation deficits, such as in California, are difficult to tie to climate change, although some have tried. Soil moisture deficits, on the other hand, are easy to tie to warmer conditions because of a strong dependence of evaporation on temperature. Hence, ag drought has become more severe, leading to increases in irrigation as well as increased fire risk. Hydrological drought can be very location-dependent. In California, given its dependence on Sierra snow pack, the real point is that temperature increases (which are higher at altitude) leads to snow deficit, regardless of any change in total precipitation.

The quoted statement is certainly false, as I am not aware of any statistically significant reduction in any measure of drought.

Overall scientific credibility: 'high'/'very high', according to 5 scientists who analyzed this article.

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Overall scientific credibility: 'high', according to 6 scientists who analyzed this article.

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Overall scientific credibility: 'high', according to 6 scientists who analyzed this article.

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Overall scientific credibility: 'very low', according to 9 scientists who analyzed this article.

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Richard Feely, Prof. of Chemical Oceanography at the NOAA Pacific Marine Environmental Laboratory:

The above statement is correct. It stems from two papers:

• The first is by Bednarsek et al (2014) in the Proceedings of the Royal Society B. From a combined survey of physical and chemical water properties and biological sampling along the Washington–Oregon–California coast in August 2011, they demonstrated that there is a strong positive correlation between the proportion of pteropod individuals with severe shell dissolution damage and the percentage of undersaturated water in the top 100m with respect to aragonite. They found 53% of onshore individuals and 24% of offshore individuals on average to have severe dissolution damage. Relative to preindustrial CO\(_2\) concentrations, the extent of undersaturated waters in the top 100m of the water column has increased over sixfold along the California Current Ecosystem (CCE). They estimated that the incidence of severe pteropod shell dissolution owing to anthropogenic Ocean Acidification has doubled in near shore habitats since pre-industrial conditions across this region and is on track to triple by 2050.

Note: I was a co-author of that paper and the chief scientist of that expedition in 2011.

• The Second paper is from Gattuso et al (2015) in Science. They evaluated the existing scientific literature on climate change and ocean acidification in the global oceans and concluded that the current emissions trajectory would rapidly and significantly alter many ecosystems and the associated services on which humans heavily depend. A reduced emissions scenario - consistent with the Copenhagen Accord’s goal of a global temperature increase of less than 2°C—is much more favorable to the ocean but still substantially alters important marine ecosystems and associated goods and services. They conclude that "any new climate regime that fails to minimize ocean impacts would be incomplete and inadequate."

Richard Feely, Prof. of Chemical Oceanography at the NOAA Pacific Marine Environmental Laboratory:

This statement is also correct.

The impact of ocean acidification on Puget Sound waters has also been well established in Feely et al (2010) and Reum et al (2014). In these papers we established that pH and aragonite saturation state values in surface and subsurface waters were substantially lower in parts of Puget Sound than would be expected from anthropogenic carbon dioxide (CO\(_2\)) uptake alone. We estimated that ocean acidification accounted for 24-49% of the pH decrease in the deep waters of the Hood Canal sub-basin of Puget Sound relative to estimated pre-industrial values. The remaining change in pH between when seawater enters the sound and when it reaches this deep basin results from remineralization of organic matter due to natural or anthropogenically stimulated respiration processes within Puget Sound. Over time, however, the relative impact of ocean acidification could increase significantly, accounting for 49-82% of the pH decrease in subsurface waters for a doubling of atmospheric CO\(_2\).

With respect to the local oyster industry, that story has been nicely described in Barton et al (2012, 2015). In these studies the authors point out that there is a clear link between natural variability in seawater aragonite saturation state due to ocean acidification and upwelling along the Oregon coast and commercial production of Pacific oyster larvae in a hatchery setting, where food and water temperatures are maintained at optimal levels, but the chemistry of incoming seawater varies. Subsequent work, in part the result of monitoring larval oysters in shellfish hatcheries, documents a mechanism for direct aragonite saturation state sensitivity in early shell formation of bivalve larvae (Waldbusser et al., 2013; 2015), responses previously thought to be related solely to changes in the organisms’ acid-base chemistry.

These findings have immediate implications for the Pacific Northwest shellfish industry, which has experienced a significant decline in seed production since 2007. In nearshore California Current surface waters off the coast of Oregon, the increase in atmospheric CO\(_2\) has shifted the median Ωarag from approximately 2.5 to 2.0 (Feely et al., 2008; Harris et al., 2013), and values of Ωarag less than 2.0 are already common throughout the spring and summer months across major sections of US Pacific coastal waters.

Overall scientific credibility: 'very low', according to the 8 scientists who analyzed this article.

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Overall scientific credibility: 'high', according to the 9 climate scientists who analyzed this article.

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Overall scientific credibility: 'high', according to the 7 climate scientists who analyzed this article.

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Gary Yohe:

A final reference is the report of the Adaptation Panel to “America’s Climate Choices” published by the National Research Council (2010). That Panel, plus the others and the Summary Document agreed with IPCC-AR4 that climate is a risk management problem. They were supported by IPCC AR4 (Synthesis Report Summary for Policymakers on page 22, the New York (City) Panel on Climate Change and others.

Gary Yohe:

See example of Katrina and other vulnerabilities in the Southeast US (NCA Highlights pages 72-73 and the more detailed commentary in the full NCA report, in the Southeast chapter. The Governor of LA and the Mayor of New Orleans had warnings, and they were still not prepared because they did not account for the tails.

Gary Yohe:

See the examples of NYC and New Jersey reactions in anticipation of Hurricane Sandy in “NCA Highlights”, particularly the Hurricane Vulnerability section on page 71, as well as the more detailed text in the background NCA complete report.

See also some adaptation responses in Southern Asia to cyclones reported in IPCC AR5 WGII; table 25-8.

Gary Yohe:

See the Special Report on Extreme Events (IPCC) and the National Climate Assessment science chapters.

For the U.S., see the series of publications in BAMS by Thomas Karl et al (e.g.). These publications summarize the results of a series of workshops in preparation for the National Climate Assessment. A summary can be found in “NCA Highlights” (Numbers 2 and 3: pages 24 and 31).

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Overall scientific credibility: 'high' to 'very high', according to 8 climate scientists who evaluated this article.

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jgdwyer:

This article accurately describes global warming and puts the news that 2014 is the hottest year on record into appropriate context. The article does a very good job of distinguishing between climate variability and climate change with helpful discussion on ENSO and the relatively cold temperatures in the Eastern United States (while staying within the bounds of the mainstream climate science understanding).

karmour:

Very good article overall. I do wish the author had fact checked the incorrect claim by Dr. Christy (that global temperatures have not changed since the end of the 20th century) prior to including his quote in the article.

aklocker:

Scientifically this article seems to be correct but it could be a bit more precise in some of its statements. One thing I like is that it mentions different opinions on some points where scientists do not agree rather than giving a biased story.

bmv:

This article does a good job of putting the 2014 temperature record in context with quotes from experts and good descriptions of relevant issues such as El Nino. References to "skeptics" were appropriately followed up by evidence of their misinterpretation/mischaracterization of the data.

aalpert:

This article provides an accurate and well supported evaluation of the finding that 2014 was the hottest year on record.

emvincent:

Overall, this article is fair in its representation of the 2014 temperature record event and in reminding the context of the long-term warming trend+natural climate variability.

alexis.tantet:

The quality of this article is overall higher than most newspaper articles on climate change as it avoids the usual pitfalls such as confusing year to year variability with long-term change. It also addresses issues prone to confusion, such as why eastern USA did not experience such a warm year as most of the globe, which can help the readers to put the science in perspective with the seasonal climate they have actually experienced. The fact that the article focuses mostly on the observational record and not on theoretical or modeling studies may be a weakness, but the scope of an article cannot be too broad.