Could Doubling CO2 Increase Earth’s Temperature by 9 Degrees C?

by Emil Morhardt

That is the assertion of a paper in Nature by Carolyn W. Snyder (Snyder, 2016) based on an analysis of the correlation between atmospheric CO2 concentrations and changes in the global average surface temperature (GAST) over the past 800,000 years. Actually the assertion is that the 95% “credible interval” is 7 to 13 degrees Celsius (12.6 to 23 degrees Fahrenheit) Yikes! Even the current scientific consensus value of something on the order of 3 C (5.4 F) (Collins et al., 2013) is frightening when you consider that the difference in the GAST between the last glacial maximum about 20,000 years ago and at present wasn’t much different than that. Continue reading

Is (Was) Global Warming on Hold?

by Emil Morhardt

A glance at the graph above, from the University of East Anglia Climatic Research Unit (http://www.cru.uea.ac.uk/), shows that the last two time periods covered (encompassing 2015) are warmer than at any time since 1850. In the prior decade, however, there was much less upward trend, feeding speculation, particularly from climate-change deniers, that all of the warming we have seen since 1900 was largely unrelated to anthropogenic carbon dioxide emissions. There was also speculation from other scientists that the apparent slowdown in warming was statistically “in the noise” and that, in time, there would be a rebound and that the monotonic upward trend since the mid-1970s would soon resume, as it now seems to have. Time will tell, of course, but mainstream climate scientists Fyfe et al. (2016) have just made a new analysis of the early 2000s warming slowdown and pronounce it real and probably largely attributable to the early 2000s’ negative phase of the Interdecadal Pacific Oscillation (IPO) in which intensification of the trade winds lowered sea surface temperatures enough to offset the warming from the ongoing increases in atmospheric greenhouse gases.  Continue reading

What Has Worked to Slow Global Warming

by Emil Morhardt

Last week, in anticipation of the United Nations climate conference in New York, The Economist concluded that the single most important action to slow global warming so far has been enactment of the Montreal protocol. Say what? This isn’t on most environmentalists’ radar as an important factor. The Montreal protocol is the 1987 international agreement to save the ozone layer by phasing out Freon and other chlorofluorocarbons used in refrigeration. But these substances are powerful greenhouse gases as well as destroyers of stratospheric ozone, and the protocol caused millions of tonnes of them not to be released into the atmosphere. The article concludes that this avoided release of the greenhouse gas equivalent of 5.6 billion tonnes (bt) of CO2. This is about twice as much avoided CO2 as the next two most effective actions, global use of nuclear power (2.8 bt) and hydroelectricity (2.2 bt), and four times that of the fourth most effective action, China’s one-child policy (1.3 bt). I’m guessing that most of the 300,000 demonstrators in New York last week are not proposing an expansion of these latter three items, but their past effectiveness does make one think. The most effective actions taken specifically to reduce energy usage and CO2 emissions have been worldwide adoption of renewables (0.6 bt), US vehicle emissions standards (0.5 bt), and Brazil forest preservation (0.4 bt). The remaining 11 items on The Economist’s list are small potatoes, totaling less than 1 bt collectively. Continue reading

Allowable Carbon Emissions Lowered by Multiple Climate Targets

by Makari Krause

Anthropogenic carbon emissions have been a large factor in climate change since the start of the industrial revolution. Scientists have become increasingly concerned with warming and other effects associated with the release of carbon into the atmosphere. Currently, most world governments have set a target that limits warming to two degrees Celsius since preindustrial times. With this target in place policies are then enacted to limit carbon emissions and hopefully to mitigate anthropogenic effects on earth’s climate. Steinacher et al. (2013) set out to show that setting a target temperature is not sufficient to control many other effects of climate change such as sea level rise and ocean acidification that also result from anthropogenic carbon emissions. They find that when targets are set for these other factors, the allowable carbon emissions are much lower than current targets based on temperature alone.

Steinacher, M., Joos, F., & Stocker, T. F., 2013. Allowable carbon emissions lowered by multiple climate targets. Nature 499(7457), 197–201. http://goo.gl/iSO7tn

 

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Climate change impacts of US reactive nitrogen

Technological advancements in agriculture, farming, and combustion technology in the United States have altered the global nitrogen cycle.   Pinder et al. (2012) developed a framework in which the oxides of nitrogen, and ammonia can be assessed for their climate change impact relative to the impact of carbon dioxide.  The gases were partitioned based on their source (combustion and agriculture) and were tested over 20 and 100 year spans.  Global warming and cooling effects were both taken into account.  The results of the study showed that under current conditions, the warming and cooling effects enacted by the reactive forms of nitrogen partially offset each other.  However, the authors note that recent trends show decreasing emissions of cooling reactive nitrogen.  — Anthony Li
Pinder R. W., Davidson E. A., Goodale C. L., Greaver T. L., Herrick J. D., Liu L. 2012. Climate change impacts of US reactive nitrogen.  Proceedings of the National Academy of Sciences of the United States of America 109 7671–7675

The metric used to measure the effect of reactive nitrogen on climate change relative to that of carbon dioxide was the Global Temperature Potential (GTPt) set to 20 and 100 years of time.  Spatial variability in nitrogen deposition was captured using the Community Multiscale Air Quality (CMAQ) model at 12 km horizontal resolution.  The model was set to 12 km in order to compensate for atmospheric nitrogen scattering by the wind.  Using the CMAQ model, the N deposition was calculated for four ecosystem types, including forest, cropland, grassland, and wetland.  N2O emissions were calculated using the Greenhouse Gas Emissions Inventory.  The researchers classified the nitrogen emissions based on their primary source; NOx was from combustion, while NH3 was from agriculture.  The analysis only considered man-made sources of nitrogen. 
The researchers found that cooling effects generally come from combustion sources, offsetting the warming effects generally coming from agricultural sources.  The largest contributors of these effects to the atmosphere were NOx and methane with their subsequent effects on ozone, radiative forcing, N2O emissions, and enhanced CO2uptake.  Combustion sources contributed to an overall cooling because their emissions of NOx can remove methane from the atmosphere by increasing hydroxyl radical concentrations.  The GTP20 found that the impact of NOx on ozone and methane is  –270 Tg CO2e and the aerosol effects are much less at a –29 Tg CO2eand –7.3 Tg CO2e for NOx and NH3, respectively.  On a 100 year basis, aerosols, ozone, and methane are negligible meaning that as the time of the analysis goes on, these compounds have less effect.  Although NOx also contributes to a warming effect by producing ozone, a greenhouse gas, its cooling effects outweigh this warming.   Agriculture sources contributed to an overall warming due to its general emissions of N2O, a potent greenhouse gas.  On a 20 year basis, the GTP20 found N2O to contribute 180–380 Tg CO2e, while on the 100 year basis, the GTP100 is found to be 160–350 Tg CO2e.  Both N2O and NOxcontributed to long-term cooling impacts due to the nitrogen enhancement (via run off) of carbon storage in forests.
The results of this study showed that the cooling effects brought by combustion emissions have negated the warming effects brought on by agricultural emissions.  While this may cause a sigh of relief for some, the authors of this paper warn of the future, noting that NOx emissions have been declining relative to CO2 so warming is likely to be the dominant effect in the future.  Another point to take with the results is that global N2O emissions are increasing, causing further imbalance to the NOx to CO2 ratio.  Our society should begin focusing on reducing N2O emissions by looking at nitrogen use-efficiency and denitrification management in the agriculture sector.  Such improvements could bring a 20–25% increase in nitrogen efficiency and a 30–50% decrease in nitrogen loses.  

Impacts of regional and global radiative forcing on regional climate change

Although regional climate change is attributable to many effects, the relevance of those effects is vague because the response to regional forcings is not adequately understood for the last century. Shindell and Faluvegi (2009) thus examined the susceptibility of various regions to changes in forcing. By determining the relationship between forcing and location reaction, and integrating observations of climate change from the twentieth century, Shindell and Faluvegi derived the importance of aerosols and resulting radiative forcing throughout time and location. This information explained that radiative forcing location influences climate response. Aerosols were proven to have great importance for both global and regional climate change. Further, the results demonstrate that, over the past three decades, the Arctic warming trend is influenced by the black carbon and aerosol emissions of the Northern Hemisphere.— Aly Stark
Shindell, D. and Faluvegi, G., 2009. Climate response to regional radiative forcing during the twentieth century. Nature Geoscience, 2, 294–300.

 Shindell and Faluvegi began by creating latitude bands and finding the response of the surface temperature to various levels of well-mixed greenhouse gases (WMGHG), ozone, and aerosols. Through this modeling, they found that when the forcing occurs within a specific latitude band, the mean temperatures follow the forcing per local unit area. Therefore, when the global mean radiative forcing is considered, the mid-latitude forcing and polar forcing must be greater than the tropical forcing (~ 2.4 and ~7 times, respectively). Higher latitude forcings are thus more sensitive to global forcing when compared to other regions.
Shindell and Faluvegi then compared the results from the modeling to the past patterns of surface temperature over various regions and time periods. These comparisons examined global and gradient responses and found significant implications for Arctic trends. The surface temperatures of the Arctic are warm until 1930, cooler from 1930–1975, and rapidly warmer onwards. Although there were differences between the observed and the recreated global and gradient responses, Shindell and Faluvegi accredit the discrepancies to internal variability and aerosol forcing. The models demonstrate a necessity for aerosol provided cooling.

            From modeling and comparisons, the results illustrate the prevalence of aerosol presence in both global and regional climate response. Further, forcing in the northern hemisphere has a particularly strong effect on the Arctic climate. As the forcing at the mid-latitude northern hemisphere oscillates between positive and negative, the temperatures of the Arctic transition from warmer to cooler. It is estimated that aerosols are one of the main contributors to the increased Arctic surface temperature; responsible for 1.09 ± 0.81° C of the 1.48 ± 0.28°C increased warming. As increased aerosol forcing continues, coupled black carbon and tropospheric ozone contributions, Arctic warming will also increase