Arctic News: sea ice

Showing posts with label sea ice. Show all posts

Sunday, November 23, 2025

The danger of abrupt eruptions of seafloor methane

Arctic

Vast amounts of methane are held in sediments at the seafloor of oceans, in the form of hydrates and in the form of free gas held underneath hydrates. Heat penetrating these sediments can destabilize hydrates and cause huge amounts of methane to erupt abruptly and enter the atmosphere.

The danger has been described many times, e.g. at the threat of seafloor methane eruptions and in the video below, by International Cryosphere Climate Initiative.

The danger is large during the Northern Summer when Arctic sea ice reaches its minimum extent and more sunlight is heating up its shallow waters. As described below, the danger is also large outside this period.

[ click on images to enlarge ]

At this time of year, Arctic sea ice is expanding rapidly, resulting in much of the Arctic Ocean getting covered with sea ice, as illustrated by the image on the right that shows Arctic sea ice concentration on November 23, 2025.

A thin layer of sea ice has sealed off the East Siberian Sea and the Laptev Sea from the atmosphere, resulting in less heat getting transferred from these seas to the atmosphere, so more heat remains in the water. This keeps the temperature of the water high, so the danger of methane eruptions remains high.

Furthermore, the temperature rise is hitting the Arctic stronger than elsewhere, resulting in more extreme weather events occurring in the Northern Hemisphere such as strong wind over the North Atlantic abruptly pushing much ocean heat from the North Atlantic into the Arctic Ocean, which can trigger destabilization of sediments at the seafloor of the Arctic Ocean at times when the ocean surface is sealed off by sea ice, reducing the ocean heat that can get transferred to the atmosphere.

Such an event occurred in February 2017 when strong wind was forecast to cause above-freezing temperatures at the North Pole, as described in an earlier post that also features the above map, indicating ocean heat getting carried along the path of the Gulf Stream into the Arctic ocean.

The image on the right shows sea surface temperatures as high as 31.1°C in the North Atlantic on November 22, 2025, while the Gulf Stream continues to push heat north toward the Arctic Ocean.

Arctic sea ice volume remains at a record daily low, as it has been for more than a year. This implies that Arctic sea ice is very thin. The image below shows Arctic sea ice volume through November 21, 2025.

Ocean heat flowing into the Arctic Ocean causes Arctic sea ice to lose thickness and volume, reducing its capacity to act as a buffer that consumes ocean heat entering the Arctic Ocean from the North Atlantic. This means that - as sea ice thickness decreases - a lot of incoming ocean heat can no longer be consumed by melting the sea ice from below, and the heat will therefore contribute to higher temperatures of the water of the Arctic Ocean. The danger of this is described in the screenshot below, which also points at the danger of a freshwater lid forming at the surface of the North Atlantic, further reducing transfer of ocean heat to the atmosphere.

[ screenshot from earlier post ]

Arctic sea ice extent was 1.91 million km² lower than 1981-2020 on November 22, 2025, a deviation from 1981-2010 of -3.36σ.

The image below shows that the global sea ice extent was 3.44 million km² lower than 1981-2020 on November 22, 2025, a deviation from 1981-2010 of -5.48σ. This is terrifying, given that we're currently in a La Niña.

[ click on images to enlarge ]

Antarctica

Sea ice extent is currently low at both poles. The low global sea ice extent at this time of year combined with high sea surface temperatures spells bad news for Antarctic sea ice, which typically reaches its minimum extent in February.

The image on the right shows Antarctic snow cover and sea ice concentration on November 23, 2025.

An Antarctic Blue Ocean Event (sea ice approaching a low of one million km²) threatens to occur in February 2026, in turn triggering an Arctic Blue Ocean Event later in 2026 while a developing El Niño is strengthening the danger, as discussed in an earlier post.

Methane

The methane danger is further illustrated by the images below. The image directly below shows methane as high as 2601 parts per billion (ppb) recorded by the NOAA 21 satellite at 399.1 mb on November 21, 2025 PM.

The image below shows hourly in situ methane measurements well above 2400 ppb. The image is adapted from an image issued by NOAA November 23, 2025, showing methane hourly averages recorded at the Barrow Atmospheric Baseline Observatory (BRW), a NOAA facility located near Utqiaġvik (formerly Barrow), Alaska, at 71.32 degrees North latitude.

Climate Emergency Declaration

UN secretary-general António Guterres recently spoke about the need for “a credible global response plan to get us on track” regarding the international goal of limiting the global temperature rise. “The science demands action, the law commands it,” Guterres said, in reference to a recent international court of justice ruling. “The economics compel it and people are calling for it.”

What could be added is that the situation is dire and unacceptably dangerous, and the precautionary principle necessitates rapid, comprehensive and effective action to reduce the damage and to improve the outlook, where needed in combination with a Climate Emergency Declaration, as described in posts such as this 2022 post and this one and as discussed in the Climate Plan group.

Links

• Permafrost Thaw is Warming the Global Climate and Impacts Communities, Health, and Oceans - by International Cryosphere Climate Initiative

https://www.youtube.com/watch?v=0uAcPf6-9-Q

• The threat of seafloor methane eruptions
https://arctic-news.blogspot.com/2025/11/the-threat-of-seafloor-methane-eruptions.html

• Warning of mass extinction of species, including humans, within one decade
https://arctic-news.blogspot.com/2017/02/warning-of-mass-extinction-of-species-including-humans-within-one-decade.html

• NOAA - sea surface temperatures

https://www.ospo.noaa.gov/products/ocean/sst/contour/index.html

• Cold freshwater lid on North Atlantic

https://arctic-news.blogspot.com/p/cold-freshwater-lid-on-north-atlantic.html

• DMI (Danish Meteorological Institute) - Arctic sea ice thickness and volume
https://ocean.dmi.dk/arctic/icethickness/thk.uk.php

• Kevin Pluck - Sea ice visuals
https://seaice.visuals.earth

• Climate Reanalyzer
https://climatereanalyzer.org

• The threat of seafloor methane eruptions

https://arctic-news.blogspot.com/2025/11/the-threat-of-seafloor-methane-eruptions.html

• Feedbacks in the Arctic
https://arctic-news.blogspot.com/p/feedbacks.html

• NOAA - HEAP/NUCAPS, NOAA-20 and NOAA-21 satellite recordings
https://www.ospo.noaa.gov/products/atmosphere/soundings/heap/nucaps/new/nucaps_products.html

• NOAA - Global Monitoring Laboratory - Data Visualisation - flask and station methane measurements
https://gml.noaa.gov/dv/iadv

• Focus on Antarctica
https://arctic-news.blogspot.com/2025/09/focus-on-antarctica.html

• Transforming Society
https://arctic-news.blogspot.com/2022/10/transforming-society.html

• Climate Plan
https://arctic-news.blogspot.com/p/climateplan.html

• Climate Emergency Declaration
https://arctic-news.blogspot.com/p/climate-emergency-declaration.html

Sunday, November 2, 2025

The threat of seafloor methane eruptions

Sea ice

Arctic sea ice volume remains at a record daily low, as it has been for more than a year. The image below shows Arctic sea ice volume through November 21, 2025.

The image below shows monthly Arctic sea ice volume in the past 25 years. Markers show April (blue) and September (red) volume, corresponding with the year's maximum and minimum. In 2025, Arctic sea ice reached a record low maximum volume as well as a record low minimum volume.

[ from earlier post ]

Warmer water flowing into the Arctic Ocean causes Arctic sea ice to lose thickness and thus volume, diminishing its capacity to act as a buffer that consumes ocean heat entering the Arctic Ocean from the North Atlantic. This means that - as sea ice thickness decreases - a lot of incoming ocean heat can no longer be consumed by melting the sea ice from below, and the heat will therefore contribute to higher temperatures of the water of the Arctic Ocean. The danger of this is described in the screenshot below.

[ screenshot from earlier post ]

Arctic sea ice extent was 1.91 million km² lower than 1981-2020 on November 21, 2025, a deviation from 1981-2010 of -3.34σ.

The image below shows that the global sea ice extent was 3.40 million km² lower than 1981-2020 on November 21, 2025, a deviation from 1981-2010 of -5.51σ. This is terrifying, given that we're currently in a La Niña.

The image below shows sea surface temperatures around Antarctica as high as -0.9°C or 30.4°F (at the green circle) on November 21, 2025. The higher the water's salt content, the lower its melting point. Seawater typically has a salinity of about 3.5% (35 grams of salt per liter of water). Sea ice starts melting when the temperature rises to about -2°C (28.4°F). By contrast, freshwater remains frozen as long as the temperature remains below 0°C (32°F).

A study led by Alessandro Silvano (2025) finds that, over the years, surface waters have become more salty.

When surface waters become saltier, they sink more readily, stirring the ocean’s layers and allowing heat from the deep to rise. This upward heat flux can melt sea ice from below, even during winter, making it harder for ice to reform. This vertical circulation also draws up more salt from deeper layers, reinforcing the cycle.

In addition to heat rising up from the deep, there is the danger that increasing amounts of both heat and carbon dioxide (CO₂), previously taken up by the ocean and stored in the deep ocean by sinking circumpolar waters, will instead remain at the surface and cause both atmospheric temperatures and CO₂ concentrations to rise.

Less sea ice extent means that less sunlight gets reflected back into space and instead gets absorbed by the sea surface, resulting in higher sea surface temperatures. Less global sea ice thus contributes to lower albedo. The image below, by Eliot Jacobson, shows the 36-month running average for the Earth albedo just hit yet another new record low, at 28.701%.

Accelerating temperature rise

The image below, created with a screenshot from a Copernicus image, shows that, over the past few months, temperatures have been rising from an anomaly (vs 1991-2020) of 0.41°C on June 23 to 0.89°C on November 21, 2025 (dark red line), getting close to if not exceeding temperature anomalies reached in 2024 (orange) and 2023 (yellow), despite the fact that we're currently in a La Niña that suppresses temperatures, whereas temperatures were raised from May 2023 through April 2024 when El Niño conditions were dominant.

The image below shows land-only monthly temperature anomalies from 1903-1915 through October 2025 (black squares). The Lowess 3-year smoothing trend (red line) points at 3°C getting crossed in the course of 2031 (dashed extension). The 1903-1915 base is not pre-industrial. Anomalies will be higher when using a genuinely pre-industrial base.

The image below shows land+ocean monthly temperature anomalies from 1903-1915 through October 2025 (black squares). The Lowess 3-year smoothing trend (red line) points at 2°C getting crossed before 2030 and 3°C getting crossed before 2040 (dashed extension). As said, the anomalies will be higher when using a genuinely pre-industrial base.

The 3°C threshold is important since humans will likely go extinct with a 3°C rise and most life on Earth will disappear with a 5°C rise, as discussed in this 2019 post.

The image below shows the October 2025 temperature anomaly from 1951-1980. Anomalies are very high, exceeding 10°C in areas over both the poles.

The combination image below highlights the October 2025 very high temperature anomalies (from 1951-1980), exceeding 10°C in areas over both the poles.

The image below shows the global monthly surface temperature anomalies from 1951-1980 through October 2025, when the anomaly was 1.37°C.

Note that the 1951-1980 base isn't pre-industrial. When using a genuinely pre-industrial base, the temperature anomaly will be much higher, well above the thresholds that politicians at the Paris Agreement pledged wouldn't be crossed.

Ominously, anomalies have kept rising over the past few months, and this occurred in the absence of El Niño conditions in 2025.

The image below shows the global temperature standard anomaly for the 12 months from November 2024 through October 2025.

The image below shows the standard deviation (Sd) anomalies from 1951-1980 of Arctic temperatures over the past few years, with a Standard Anomaly of 6.68σ reached in October 2025.

The image below shows the standard deviation (Sd) anomalies from 1951-1980 of Arctic temperatures over the past few years, with a Standard deviation Anomaly of 4.59σ reached in October 2025.

Sea surface temperature anomalies

The image below shows monthly sea surface temperature anomalies from 1951-1980 through September 2025, when the anomaly was 0.74°C. The image also shows that the anomaly in September 2023 was 0.901°C.

The image below shows the standard deviation from 1951-1980 of the monthly sea surface temperature through September 2025, when it was 8.045σ. The image also shows that the standard deviation in August 2023 was 10.148σ.

In statistics, the empirical rule states that in a normal distribution, 68% of the observed data will occur within one standard deviation (1σ), 95% within two standard deviations (2σ), and 99.7% within three standard deviations (3σ) of the mean. A 4σ event indicates that the observed result is 4 standard deviations (4σ) away from the expected mean. In a normal distribution, 99.993666% of data points would fall within this range. The chance for data to fall outside of 4σ is thus infinitesimally small.

Meanwhile, sea surface temperatures have remained very high. The image below shows sea surface temperature anomalies from 1981-2011 in the Northern Hemisphere, with anomalies as high as 9°C or 13.6°F visible in the path of the Gulf Stream (at the green circle).

Wild weather swings

[ 24+°C anomaly over part of Greenland ]

Wild weather swings are striking the world with accelerating intensity and ferocity. More than 1.4 million evacuated as second typhoon in a week slams into the Philippines, reports CNN.

The image on the right shows temperature anomalies higher than 24°C at 2m in an area over Greenland on November 13, 2025.

The image below shows strong wind over Baffin Bay boosting temperatures over Greenland to levels as high as 12.9°C or 55.1°F (at the green circle) at 1000 hPa on November 13, 2025, as strong wind pushes warm air over Greenland, while cold Arctic air gets pushed down toward England.

ENSO outlook, next El Niño likely to be devastating

[ click on images to enlarge ]

Currently, global sea ice is low and temperatures are high, despite the fact that La Niña conditions are suppressing the temperature. This should constitute a strong warning that temperatures look set to accelerate dramatically with the development of the next El Niño, likely to occur in the course of 2026.

According to a NOAA analysis issued Nov 13, 2025, La Niña continued over the past month, and La Niña is favored to continue into the Northern Hemisphere winter, with a transition to ENSO-neutral most likely in January-March 2026 (61% chance, image right).

ENSO (El Niño-Southern Oscillation) has three states: El Niño (when temperatures are higher than average), La Niña (when temperatures are suppressed), and a neutral state.

The image on the right, adapted from a November 2025 NOAA image, gives an ENSO outlook (CFSv2 ensemble mean, black dashed line) that favors La Niña to persist into the early Northern Hemisphere winter 2025-26, implying that temperatures will remain suppressed until early 2026.

[ click on images to enlarge ]

The image on the right, adapted from ECMWF, shows the ENSO anomaly and forecast for developments in Niño3.4 through November 2026, indicating that the next El Niño will emerge and grow in strength in the course of 2026.

The depth of the current La Niña is illustrated by the image below. The image shows strongly negative sea surface temperature anomalies (SSTA, NOAA OISST v2.1 data) in the Niño3.4 area in the Central Pacific, with a -0.98°C anomaly vs 1991-2020 on November 18, 2025, while the inset shows global SSTA vs 1991-2020 on November 18, 2025.

NOAA considers La Niña conditions to occur when a one-month negative sea surface temperature anomaly of -0.5° C or less is observed in the Niño-3.4 region of the equatorial Pacific Ocean (5°N-5°S, 120°W-170°W) and an expectation that the 3-month Oceanic Niño Index (ONI) threshold will be met, and an atmospheric response typically associated with La Niña is observed over the equatorial Pacific Ocean.

The graph below uses CDAS (Climate Data Assimilation System) data showing an anomaly of -1.202ºC on November 15, 2025.

The CDAS analysis below shows very low sea surface temperature anomalies in the Niño3.4 area on November 15, 2025.

The CanSIPS forecast for March 2026 below shows high sea surface temperature anomalies in the central Pacific Ocean, indicating development of the next El Niño. The low sea surface temperature anomalies around Antarctica indicate areas where heavy melting will likely have taken place by March 2026.

Antarctica

The image on the right shows Antarctic snow cover and sea ice concentration on November 21, 2025.

The combination image below shows Antarctic sea ice concentration on November 19, 2025 (left) and Antarctic sea ice thickness on November 19, 2025 (right).

The comparison image below shows the thickness of the Antarctic sea ice on October 6 and on November 21, 2025.

An Antarctic Blue Ocean Event (sea ice approaching a low of one million km²) threatens to occur in February 2026, triggering an Arctic Blue Ocean Event later in 2026 while a developing El Niño is strengthening the danger. Ominously, the forecast of sea surface temperature anomalies for August 2026 below looks grim.

The methane danger

This increases the danger that massive amounts of methane will erupt from the seafloor in 2026, further accelerating the temperature rise.

The methane danger is further illustrated by the images below. The image directly below shows methane as high as 2620 parts per billion (ppb) recorded by the NOAA 20 satellite at 487.2 mb on November 5, 2025 AM.

The image below shows hourly methane measurements well above 2400 ppb. The image is adapted from an image issued by NOAA November 9, 2025, showing methane hourly averages recorded in situ at the Barrow Atmospheric Baseline Observatory (BRW), a NOAA facility located near Utqiaġvik (formerly Barrow), Alaska, at 71.32 degrees North latitude.

The image below is a similar image, this time showing that the monthly average methane recorded at the same station is about 2050 ppb.

In the video below, Guy McPherson discussed our predicament.

Links

• DMI (Danish Meteorological Institute) - Arctic sea ice thickness and volume
https://ocean.dmi.dk/arctic/icethickness/thk.uk.php

• Kevin Pluck - Sea ice visuals
https://seaice.visuals.earth

• Climate Reanalyzer

https://climatereanalyzer.org

• nullschool.net

https://earth.nullschool.net

• NOAA - ENSO evolution
https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

• NOAA (National Oceanic and Atmospheric Administration) - Climate Prediction Center

https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml

• ECMWF (European Centre for Medium-Range Weather Forecasts) - charts

https://charts.ecmwf.int/products/seasonal_system5_nino_annual_plumes

• NASA (National Aeronautics and Space Administration) - GISS Surface Temperature Analysis

https://data.giss.nasa.gov/gistemp/graphs_v4/customize.html

• Pre-industrial

https://arctic-news.blogspot.com/p/pre-industrial.html

• When Will We Die?
https://arctic-news.blogspot.com/2019/06/when-will-we-die.html

• Tropicaltidbits
https://www.tropicaltidbits.com

• Feedbacks in the Arctic
https://arctic-news.blogspot.com/p/feedbacks.html

• NOAA - Global Monitoring Laboratory - Data Visualisation - flask and station methane measurements
https://gml.noaa.gov/dv/iadv

• Focus on Antarctica

https://arctic-news.blogspot.com/2025/09/focus-on-antarctica.html

• Transforming Society
https://arctic-news.blogspot.com/2022/10/transforming-society.html

• Climate Plan
https://arctic-news.blogspot.com/p/climateplan.html

• Science Snippets: The Living Planet on the Brink - by Guy McPherson
https://guymcpherson.substack.com/p/science-snippets-earth-on-the-brink
video at:
https://www.youtube.com/watch?v=iXXSWNehxZs

• Climate Emergency Declaration
https://arctic-news.blogspot.com/p/climate-emergency-declaration.html

Saturday, October 25, 2025

Antarctic sea ice area reaches record daily low

Antarctic sea ice area remained at a record daily low on October 24, 2025, following a record daily low on October 23, 2025. Antarctic sea ice area was 12.40 million km² on October 24, 2025, a deviation from 1981-2010 of -3.57σ, as illustrated by the image below.

The above image also shows that Antarctic sea ice reached a record low area of 1.09 million km² on February 24, 2023, close to a Blue Ocean Event and corresponding with a deviation of -2.86σ, i.e. smaller than the deviation of -3.57σ reached recently (on October 23, 2025).

Global sea ice extent

Low sea ice extent means that less sunlight gets reflected back into space and instead gets absorbed by the sea surface, resulting in high sea surface temperatures. Currently, sea ice is low at both poles. The low global sea ice extent at this time of year spells bad news for Antarctic sea ice, which typically reaches its minimum extent in February.

The image below shows that the standard deviation from 1981-2010 of the global sea ice extent was -6.89σ on October 31, 2025, which is remarkable given the absence of El Niño conditions in 2025.

Arctic sea ice volume

Meanwhile, Arctic sea ice volume remains at a record daily low, as it has been for more than a year. The image below shows Arctic sea ice volume through October 31, 2025.

High temperatures

Low sea ice and polar amplification of the temperature rise contribute to high air temperatures at both poles. The image below shows the September 2025 temperature anomaly compared to 1951-1980.

[ from earlier post ]

The low sea ice and the high temperatures are even more remarkable given the absence of El Niño conditions.

[ click on images to enlarge ]

Little sunlight is yet reaching the South Pole at this time of year. While temperatures over Antarctica are still well below zero °C, they are rising fast. Antarctic temperature anomalies were high in September 2025 (see the above image) and in October 2025 (see the image below).

The image on the right, adapted from NOAA, shows the ENSO outlook (CFSv2 ensemble mean, black dashed line) favors La Niña persisting into the early Northern Hemisphere winter 2025-26.

[ image from earlier post ]

The image on the right, adapted from ECMWF, shows the ENSO anomaly and forecast for developments in Niño3.4 through August 2026, indicating that the next El Niño will emerge and grow in strength in the course of 2026.

A record high daily Antarctic temperature was reached on October 26, 2025, corresponding with a temperature anomaly of +5.08°C versus 1979-2000, as illustrated by the image below.

The inset on the image below shows high temperature anomalies at both poles vs 1991-2020 on October 26, 2025.

A record high daily Arctic temperature was reached on October 27, 2025, corresponding with a temperature anomaly of +5.99°C versus 1979-2000, as illustrated by the image below. The inset on the image below shows high temperature anomalies at both poles vs 1991-2020 on October 27, 2025.

Global temperature anomalies have been rising over the past few months, and reached a record daily high of 15.04°C, an anomaly of +0.93°C versus 1991-2020, on October 25, 2025, as illustrated by the image below.

The following day, on October 26, 2025, the temperature reached another daily high. The image below shows temperature anomalies in red from January 1, 2023, through October 26, 2025, with a non-linear (polynomial) trend added in blue.

Note that the anomalies on the above images are calculated from 1991-2020. When calculated from pre-industrial, the anomalies will be much higher, as discussed in earlier post such as this one.

The image below shows a forecast of the temperature anomaly vs 1981-2010 for November 2025.

The image below shows a forecast of the temperature anomaly versus 1981-2010 for December 2025.

The situation is dire. An Antarctic Blue Ocean Event (sea ice approaching a low of one million km²) threatens to occur in February 2026, triggering an Arctic Blue Ocean Event later in 2026 while the next El Niño is strengthening, which comes with a huge danger of massive amounts of methane erupting from the seafloor.

Southern Ocean sea surface getting more salty

High temperature anomalies are present at both the poles, as illustrated by the image below that shows the situation on October 25, 2025.

High temperatures come with Jet Stream distortion on October 25, 2025, as illustrated by the image below that shows the Jet Stream (at 500 hPa) moving deep over Antarctica.

This came with high precipitable water anomalies over Antarctica, as illustrated by the image below.

This came with snowfall over Antarctica, as illustrated by the image below.

The danger has been discussed in earlier posts such as this one. The increased snowfall thickens the snow on Antarctica with only little freshwater returning to the ocean. As a result, the Southern Ocean surface is getting more salty, and as also discussed in an earlier post, saltier surface waters sink more readily, allowing heat from the deep to rise, which can melt Antarctic sea ice from below, even during winter, making it harder for ice to reform. This vertical circulation also draws up more salt from deeper layers, reinforcing the cycle.

This leads to a loss of sea ice (and thus loss of albedo and latent heat buffer), as well as less heat getting transferred from the atmosphere into the Southern ocean, while more heat can be transferred from the Southern Ocean to the atmosphere.

The methane danger

The methane danger is illustrated by the image below, adapted from an image issued by NOAA October 29, 2025, showing hourly methane averages recorded at the Barrow Atmospheric Baseline Observatory (BRW), a NOAA facility located near Utqiaġvik (formerly Barrow), Alaska, at 71.32 degrees North.

Danger assessment

A state of emergency is typically declared after a disaster hits a specific area. The idea is that repairs or replacement of buildings, equipment and infrastructure can quickly restore the situation to what it previously was. Insurance companies have traditionally determined premiums for insurance policies by calculating the risk of events by their severity and probability.

However, extreme weather events can increasingly be expected to occur more frequently and important considerations are the intensity and severity at which one specific place gets hit by an event, as well as ubiquity and imminence of such events. As temperatures rise, more extreme weather events can be expected to occur with greater intensity, more frequently, over larger areas, with longer duration and to become more ubiquitous and follow each other up with increasing if not accelerating rapidity.

As the likeliness of a huge and accelerating temperature rise, the severity of its impact, and the ubiquity and the imminence with which it will strike all become more manifest—the more sobering it is to realize that a mere 3°C rise may suffice to cause human extinction.