RealClimate (@realclimate) — Bluesky Profile

11 months ago

RealClimate: The Alsup Aftermath RealClimate: The presentations from the Climate Science tutorial last month have all been posted (links below), and Myles Allen (the first presenter for the plaintiffs) gives his impression of the eve...

The Alsup Aftermath - 25 APR 2018 www.realclimate.org/index.php/ar... #climatechange #science

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11 months ago

The Silurian Hypothesis (preprint) is the idea if industrial civilization had arisen on Earth prior to the existence of hominids, what traces would be left that could be detectable now? As a starting point, we explore what the traces of the Anthropocene will be in millions of years – carbon isotope changes, global warming, increased sedimentation, spikes in heavy metal concentrations, plastics and more – and then look at previous examples of similar events in the geological record. What is unique about our presence on Earth and what might be common to any industrial civilization? Can we rule out similar causes?

The Silurian Hypothesis - 17 APR 2018 www.realclimate.org/index.php/ar... #climatechange #science

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11 months ago

Fig. 1 Trends in sea surface temperatures. Left: in the climate model CM2.6 in a scenario with a doubling of the amount of CO2 in the air. Right: in the observation data from 1870 to the present day. In order to make the trends comparable despite the different periods and CO2 increases, they were divided by the globally averaged warming trend, i.e. all values above 1 show an above-average warming (orange-red), values below 1 a below-average warming, negative values a cooling. Due to the limited availability of ship measurements, the measurement data are much more “blurred” than the high-resolution model data. Graph: Levke Caesar

Fig. 2 Time evolution of the Atlantic overturning circulation reconstructed from different data types since 1700. The scales on the left and right indicate the units of the different data types. The blue curve was shifted to the right by 12 years since Thornalley found the best correlation with temperature with this lag. Makes sense: it takes a while until a change in currents alters the temperatures. Graph: Levke Caesar.

Stronger evidence for a weaker Atlantic overturning circulation
11 APR 2018 - www.realclimate.org/index.php/ar... #climatechange #science #climatechange #science

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11 months ago

RealClimate: Harde Times RealClimate: Readers may recall a post a year ago about a nonsense paper by that appeared in Global and Planetary Change. We reported too on the crowd-sourced rebuttal led by that was published last O...

Harde Times - 4 APR 2018 www.realclimate.org/index.php/ar... #climatechange #science

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11 months ago

RealClimate: Unforced Variations: Apr 2018 RealClimate: This month's open thread for general climate science discussions.

Unforced Variations: Apr 2018 - 1 APR 2018 www.realclimate.org/index.php/ar... #climatechange #science

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11 months ago

Main sources of human CO2 emissions are fossil fuel burning and (net) deforestation. This figure is from the Global Carbon Project in 2017.

Prior to ~1750, atmospheric CO2 had been stable (within a few ppm) for millenia sustained by a balance between natural sources and sinks. This figure shows the changes seen in ice cores and the instrumental record.

The Earth’s surface emits infrared radiation. This is absorbed by greenhouse gases, which through collisions with other molecules cause the atmosphere to heat up. Emission from greenhouse gases (in all directions, including downwards) adds to the warming at the surface.

The figure shows the easiest mathematical description of the greenhouse effect. The downward radiation from greenhouse gases can be easily measured at the surface in nights under clear skies and no other heat sources in the atmosphere (e.g. Philipona and Dürr, 2004).

The US National Climate Assessment attribution statement is a bit more specific than the one in IPCC:

The likely range of the human contribution to the global mean temperature increase over the period 1951–2010 is 1.1° to 1.4°F (0.6° to 0.8°C), and the central estimate of the observed warming of 1.2°F (0.65°C) lies within this range (high confidence). This translates to a likely human contribution of 93%–123% of the observed 1951–2010 change. It is extremely likely that more than half of the global mean temperature increase since 1951 was caused by human influence on climate (high confidence). The likely contributions of natural forcing and internal variability to global temperature change over that period are minor (high confidence).

This summary graphic is useful:

Basically, all of the warming trend in the last ~60yrs is anthropogenic (a combination of greenhouse gases, aerosols, land use change, ozone etc.). To get a sense of the breakdown of that per contribution for the global mean temperature, and over a longer time-period, the Bloomberg data visualization, using data from GISS simulations is very useful.

This is the biggie. What is the attribution for the temperature trends in recent decades? The question doesn’t specify a time-scale, so let’s assume either the last 60 years or so (which corresponds to the period specifically addressed by the IPCC, or the whole difference between now and the ‘pre-industrial’ (say the decades around 1850) (differences as a function of baseline are minimal). For the period since 1950, all credible studies are in accord with the IPCC AR5 statement:
It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together. The best estimate of the human-induced contribution to warming is similar to the observed warming over this period.

Alsup asks for answers - 11 MAR 2018 www.realclimate.org/index.php/ar... #climatechange #science

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11 months ago

RealClimate: Forced responses: Mar 2018 RealClimate: This month's open thread on responses to climate change (politics, adaptation, mitigation etc.). Please stay focused on the overall topic. Digressions into the nature and history of commu...

Forced responses: Mar 2018 - 1 MAR 2018 www.realclimate.org/index.php/ar... #climatechange #science

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11 months ago

RealClimate: Unforced variations: Mar 2018 RealClimate: This month's open thread for climate science related items. The open thread for responses to climate change is here.

Unforced variations: Mar 2018 - 28 FEB 2018 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

Figure 1: The seven longest data sets of Minnesotan lake “ice out” dates (with data back to at least 1900). Ice out date is shown relative to the vernal equinox (see below for details). Red lines are loess ~30yr smooths.

There are good data sets for dozens of other lakes in North America, notably ice duration from Lakes Mendota and Monona in Wisconsin. Note that ice duration is slightly less noisy dataset than ice out.

These data are nominally collated by the Global Lake and River Ice Phenology Database, but it isn’t that up-to-date, though it does include a lot of long records from Europe.

One other notable lake is Lake Winnipesaukee in NH (h/t David Appell), which has records from 1887 and a betting pool.

More ice-out and skating day data sets - 26 FEB 2018 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

I’ve been interested in indirect climate-related datasets for a while (for instance, the Nenana Ice Classic). One that I was reminded of yesterday is the 48-year series of openings and closings of the Rideau Canal Skateway in Ottawa.

Rideau Canal Skateway. Lauren Bath
Since 1971, the National Capital Commission (NCC) in Ottawa has (once the ice is thick enough for safe skating) methodically tried to keep the frozen canal available for ice skaters (by clearing snow, smoothing surfaces, filling cracks etc.). This is possible only if the weather permits – first by being cold enough to sufficiently freeze the ice, and second by not being warm enough to melt the ice surface as the season progresses. Apart from the first season, which was not planned ahead of time, each year since has been anticipated to start in the second half of December (or early January) and ideally extends to March.

Updating the Brammer et al graph to 2018 (including the record shortest season in 2016) is straightforward:

Rideau Canal Skateway. Brammer et al (updated)
As expected, there are clear trends in season length (a reduction of ~23±11 days (95% CI) since 1972), and while there are decreases in skating days, they aren’t significant due to the too short period (similarly with the available opening/closing dates). There is of course the possibility on non-climatic artifacts. Increasing skill/experience of the Skateway managers might prolong the season, while decreasing tolerances for risk(?) might shorten it. These are issues that are hard to quantify without much greater amounts of the meta-data associated with the opening and closing.

Nevertheless, we have another independent dataset which conforms to our expectations that outdoor ice in North America is suffering.

Rideau Canal Skateway - 22 FEB 2018 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

RealClimate: Unforced variations: Feb 2018 RealClimate: This month’s open thread for climate science topics. Note that discussions about mitigation and/or adaptation should be on the Forced Responses thread. Let’s try and avoid a Groundhog Day...

Unforced variations: Feb 2018 - 2 FEB 2018 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

RealClimate: IPCC Communication handbook RealClimate: A new handbook on science communication came out from IPCC this week. Nominally it's for climate science related communications, but it has a wider application as well. This arose mainly ...

IPCC Communication handbook - 31 JAN 2018 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

Fig. 1 Perhaps the most important scientific measurement series of the 20th century: the CO2 concentration of the atmosphere, measured on Mauna Loa in Hawaii. Other stations of the global CO2 measurement network show almost exactly the same; the most important regional variation is the greatly subdued seasonal cycle at stations in the southern hemisphere. This seasonal variation is mainly due to the “inhaling and exhaling” of the forests over the year on the land masses of the northern hemisphere. Source (updated daily): Scripps Institution of Oceanography.

Fig. 4 CO2 budget for 2007-2016, showing the various net sources and sinks. The figures here are expressed in gigatons of CO2 and not in gigatons of carbon as in Fig. 3. The conversion factor is 44/12 (molecular weight of CO2 divided by atomic weight of carbon). Source: Global Carbon Project.

Fig. 3 Scheme of the global carbon cycle. Values for the carbon stocks are given in Gt C (ie, billions of tonnes of carbon) (bold numbers). Values for average carbon fluxes are given in Gt C per year (normal numbers). Source: WBGU 2006 . (A similar graph can also be found at Wikipedia.) Since this graph was prepared, anthropogenic emissions and the atmospheric CO2 content have increased further, see Figs 4 and 5, but I like the simplicity of this graph.

Fig. 6 Excerpt from the New York Times of 6 November 1997

The text to go with it read:

While most of the CO2 emitted by far is the result of natural phenomena – namely respiration and decomposition, most attention has centered on the three to four percent related to human activities – burning of fossil fuels, deforestation.

That is pretty clever and could hardly be an accident. The impression is given that human emissions are not a big deal and only responsible for a small percentage of the CO2 increase in the atmosphere – but without explicitly saying that. In my view the authors of this piece knew that this idea is plain wrong, so they did not say it but preferred to insinuate it. A recent publication by Geoffrey Supran and Naomi Oreskes in Environmental Research Letters has systematically assessed ExxonMobil’s climate change communications during 1977–2014 and found:

We conclude that ExxonMobil contributed to advancing climate science—by way of its scientists’ academic publications—but promoted doubt about it in advertorials. Given this discrepancy, we conclude that ExxonMobil misled the public.

The global CO2 rise: the facts, Exxon and the favorite denial tricks - 25 JAN 2018 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

Figure 1. Test of the Hasselmann model through a regression analysis, where the coloured curves are the best-fit modelled values for Q based on the Hasselmann model and global mean temperatures (PDF).

Figure 2. The regression coefficients. Negative values for C are unphysical and suggest that the Hasselmann model is far from perfect. The estimated error margins for C are substantial, however, and also include positive values. Blue point shows the estimates for NCEP/NCAR reanalysis. The shaded areas cover the best estimates plus/minus two standard errors (PDF).

Figure 3. The area of Earth’s surface with valid temperature data (PDF).

The claim of reduced uncertainty for equilibrium climate sensitivity is premature - 21 JAN 2018 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

2017 temperature summary
19 JAN 2018 BY GAVIN

This is a thread to discuss the surface temperature records that were all released yesterday (Jan 18). There is far too much data-vizualization on this to link to, but feel free to do so in the comments. Bottom line? It’s still getting warmer.

2017 temperature summary - 19 JAN 2018 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

RealClimate: Forced Responses: Jan 2018 RealClimate: This is a new class of open thread for discussions of climate solutions, mitigation and adaptation. As always, please be respectful of other commentators and try to avoid using repetition...

Forced Responses: Jan 2018 - 1 JAN 2018 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

RealClimate: Unforced Variations: Jan 2018 RealClimate: Happy new year, and a happy new open thread. In response to some the comments we've been getting about previous open threads, we are going to try separating out OT comments on mitigation/...

Unforced Variations: Jan 2018 - 1 JAN 2018 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

If you think you know why NASA did not report the discovery of the Antarctic polar ozone hole in 1984 before the publication of Farman et al in May 1985, you might well be wrong.

One of the most fun things in research is what happens when you try and find a reference to a commonly-known fact and slowly discover that your “fact” is not actually that factual, and that the real story is more interesting than you imagined…

Joe Farman and colleagues (BAS)Here is the standard story (one I’ve told repeatedly myself): The publication in 1985 by scientists from the British Antarctic Survey working at Halley Station (right) of observations of extremely low ozone values in Oct 1983 (SH springtime) came as a huge shock to the scientific community. Given that NASA had been monitoring ozone by satellite using the NIMBUS instruments since the late 1970s, people were surprised that this had not been reported already. NASA scientists went back to the satellite data and found that anomalously low values had been rejected as bad data and were not included in the analyses. After reprocessing the data with this flag removed, the trends became clear and the confirmation of ground-based data was reported in the NY Times in Nov 1985 and published formally the next year (Stolarski et al., 1986).

This is mostly true, but not quite…

It is true that the Quality Control (QC) flag on the retrieval was set whenever the inferred ozone level dropped below 180 Dobson Units [1 DU is equivalent to a 0.01mm thick pure ozone layer at standard temperature and pressure]. Prior to 1983, there had never been an observation below 200 DU and so values lower than 180 DU were out of calibration range for the sensor.

However, it wasn’t true that no-one at NASA had noticed.

What did NASA know? and when did they know it? - 24 DEC 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

RealClimate: Fall AGU 2017 RealClimate: It's that time of year again. #AGU17 is from Dec 11 to Dec 16 in New Orleans (the traditional venue in San Francisco is undergoing renovations). As in previous years, there will be extens...

Fall AGU 2017 - 7 DEC 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

RealClimate: Unforced Variations: Dec 2017 RealClimate: Last open-thread of the year. Tips for new books for people to read over the holidays? Highlights of Fall AGU (Dec 11-15, New Orleans)? Requests for what should be in the end of year upda...

Unforced Variations: Dec 2017 - 3 DEC 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

$Historgam of 24-hr precipitation measured at Bjørnholt in a forest near Oslo. There will always be some clutter at the upper end of plots like these because there are so few data points representing these extreme values. The nice thing with the exponential distribution (which is a particular case of the gamma function) is that it only requires one parameter to specify the mathematical curve: it’s the inverse of the mean value \mu. I then used Bayes’ theorem to account for dry and wet days, where the probability for rainfall was taken to be the wet-day frequency f_w. The advantage of this approach is that I now had two parameters which were easy to estimate: the wet-day mean precipitation (or mean rainfall intensity) \mu and the wet-day frequency f_w.$ $Figure 1. A comparison between probabilities estimated with the rain equation and the observed fraction of events with more than 30 mm rain in Groningen in the Netherlands. Here H(X - x) refers to the Heaviside function, which is a mathematical way of expressing that I only counted the number of events with more than 30 mm/day each year in the observations (the plot was made with the R-package esd and the command test. rainequation(loc='GRONINGEN-1',threshold=20)).$ $Figure 2. A scatter plot of probabilities and corresponding fractions of events from long rain gauge records in Europe, based on the wet-day mean precipitation and frequency from the observations (the plot was made with the R-package esd and the command scatterplot.rainequation()).$

A brief review of rainfall statistics - 21 NOV 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

While many instruments can be used to detect sea ice, the continuity required for long-term climate monitoring makes it vital that the different products are cross-calibrated and have similar characteristics to be useful. The closest instruments to the those on the DMSP satellites are the radiometers (MWRI) on the Chinese Feng Yun-3 series of satellites. Unfortunately, again because of Congress, NASA collaborations with China are restricted and since the sea ice work at NSIDC is funded by NASA, that might prevent this source of data being used in the US (though presumably non-US colleagues would not have this problem).

Another possibility is the Japanese satellite GCOM-W1 which has a more advanced AMSR2 instrument (in space since 2012, and has also passed it’s design lifetime), but the merge of this data with the DMSP satellites is still a work in progress. This is being used for the Bremen University sea ice maps though.

Differences in views from passive microwave instruments (SSMI vs. AMSR2) via Arctic Roos.
Unfortunately, the next scheduled passive microwave sensor to be launched is not until 2022 on the European Space Agency’s 2nd Generation MetOp satellite, and will need a year’s overlap with an existing satellite to be optimally calibrated. Thus the likelihood of a gap in the record developing before then is very high.

O Say can you See Ice… - 6 NOV 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

RealClimate: Unforced variations: Nov 2017 RealClimate: This month's open thread. Lawsuits about scientific disputes, the new Climate Science Special Report from the National Climate Assessment, and (imminently) the WMO State of the Climate st...

Unforced variations: Nov 2017 - 4 NOV 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

Fig. 1 GISTEMP global temperature data, in 12-months running average (anomalies relative to the first 30 years). The data are available monthly and averaging over 12 months removes a considerable amount of month-to-month ‘noise’. Showing only calendar-year averages would lose some information – e.g. it would only fully show peaks in temperature if by chance the maxima aligned with the calendar year.

Fig. 2 The two El Niño peaks in global temperature from Fig. 1, zoomed in and overlayed by shifting the 2016 peak back in time by 14 years and down by 0.4 °C. The darker red curve is the 2016 peak, as in Fig. 1.

El Niño and the record years 1998 and 2016 - 4 NOV 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

Fig. Extreme heat and drought impacted the carbon cycle in tropical forests differently in different regions, leading to the fastest growth rate of CO2 in at least 10,000 years. (NASA/JPL-Caltech).

OCO-2 has given us two revolutionary new ways to understand the effects of drought and heat on tropical forests. The instrument directly measures CO2 over these regions thousands of times every day (Crisp et al, 2004). These column-averaged concentration retrievals respond to the net amount of CO2 passing in and out of the atmosphere under the instrument. OCO-2 also senses the rate of photosynthesis by detecting fluorescent chlorophyll in the trees themselves (Frankenberg et al, 2011). Liu et al used observations of CO from the MOPITT instrument aboard NASA’s Terra satellite to identify CO2 released from upwind wildfires. They used solar-induced chlorophyll fluorescence (SIF) to quantify changes in plant photosynthesis (also called gross primary production, GPP). Their results include time-resolved maps of the sources and sinks of atmospheric CO2 that are optimally consistent with both mechanistic forward models and the CO2, CO, and SIF observed by the satellite instruments.

O Say Can You CO2… - 12 OCT 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

Figure 1: (a) shows temperature change in the CMIP5 simulations relative to observed temperature products. Grey regions show model range under historical and RCP8.5 forcing relative to a 1900-1940 baseline. Right-hand axis shows temperatures relative to 1861-1880 (offset using HadCRUT4 temperature difference). (b) shows temperature change as a function of cumulative emissions. Black solid line shows the CMIP5 historical mean, and black dashed is the RCP8.5 projection. Colored lines represent regression reconstructions as in Otto (2015) using observational temperatures from HadCRUT4 and GISTEMP, with cumulative emissions from the Global Carbon Project. Colored points show individual years from observations.
The choice of temperature data

We can illustrate how these effects might influence the Millar analysis by repeating the calculation with alternative temperature data. Their approach requires an estimate of the forced global mean temperature in a given year (excluding any natural variability), which are derived from Otto et al (2015), who employ a regression approach to reconstruct a prediction of global mean temperatures as a function of anthropogenic and natural forcing agents. In Fig. 1(a), we apply the Otto approach to data from GISTEMP as well as the HadCRUT4 product used in the original paper – again using data up to 2014. Although the HadCRUT4 forced Otto-style reconstruction suggests 2014 temperatures were less than the 25th percentile of the CMIP5 distribution, following the same procedure with GISTEMP yields 2014 temperatures of 1.08K – corresponding to the 58th percentile of the CMIP5 distribution.

Figure 2: (a) Temperatures of reconstructed global mean temperature in 2014 for the CESM large ensemble following the Otto (2015) regression methodology, plotted as a function of average global mean temperature in the years 2005-2014. (b) correlation between mean grid-point temperatures in 2005-2014 and reconstructed global mean temperature in 2014, ellipses show regions proposed for Pacific Climate Index. (c) CESM large ensemble reconstructed global mean temperature in 2014 as a function of Pacific Climate Index. Vertical lines show index values for observations in period 2005-2014 (solid) and historical (dashed).
In order to assess how this potential bias might have been manifested in the historical record, we construct an index of this pattern using regions of strong positive and negative correlation to the inferred forced warming. Fig 2(b) shows the correlation between inferred forced 2014 temperature and 2005-2014 temperatures, showing a pattern reminiscent of the Interdecadal Pacific Oscillation, a leading mode of unforced variability. The warming estimate is positively correlated with central Pacific temperatures, and negatively correlated with South Pacific temperatures. An index of the difference between these regions is shown in Fig. 1(c) for observations and models. Both HadCRUT and GISTEMP suggest strongly negative index values for the period 2005-2014, suggesting a potential cold bias in the warming estimate due to natural variability of 0.1˚C (with 5-95% values of 0.05-0.15˚C).

1.5ºC: Geophysically impossible or not? - 4 OCT 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

…the Harde they fall. Back in February we highlighted an obviously wrong paper by Harde which purported to scrutinize the carbon cycle. Well, thanks to a crowd sourced effort which we helped instigate, a comprehensive scru...

…the Harde they fall. - 4 OCT 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

Unforced variations: Oct 2017 This month's open thread. Carbon budgets, Arctic sea ice minimum, methane emissions, hurricanes, volcanic impacts on climate... Please try and stick to these or similar topics.

Unforced variations: Oct 2017 - 1 OCT 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

Figure: Difference between modeled and observed warming in 2015, with respect to the 1861-1880 average. Observational data has had short-term variability removed per the Otto et al 2015 approach used in the Millar et al 2017. Both RCP4.5 CMIP5 multimodel mean surface air temperatures (via KNMI) and blended surface air/ocean temperatures (via Cowtan et al 2015) are shown – the latter provide the proper “apples-to-apples” comparison. Chart by Carbon Brief.

Is there really still a chance for staying below 1.5 °C global warming? - 22 SEP 2017 www.realclimate.org/index.php/ar... #climatechange #science

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1 year ago

The Helix at DCU was the main venue of #EMS2017

Impressions from the European Meteorological Society’s annual meeting in Dublin - 14 SEP 2017 www.realclimate.org/index.php/ar... #climatechange #science

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