Category: Climate Change

Greenhouse gases, particulates, radiative forcing, global temperature; cryosphere

The next ten years…

One would think the latest reports documenting the lack of action regarding climate change, the continued and accelerating changes to the oceans and cryosphere, the deteriorating condition of the Great Barrier Reef, and the astonishing decline in avian populations along with the ongoing extinction of numerous other plant and animal species, should serve to focus global attention on planetary change in the Anthropocene.  Unfortunately, it would appear that business as usual will be the most likely outcome of all these reports, despite much wringing of hands, gloomy predictions and opining of pundits, experts and the like. 

A hallmark of the Anthropocene is the observably (much!) higher rate of change in many Earth system processes as compared to “background” rates determined from historical records. This acceleration has been well documented, but very poorly communicated to the general public and largely ignored by decision makers.  Rising concentrations of carbon dioxide, increasing sea and land temperatures, accelerated melt rates of sea ice, permafrost and ice sheets, along with rising sea level, inform us that a critical fork in the road lies ahead.  Ignore these signposts and there will be no opportunity to even make a choice as to which road we take—the decision will have been already made.

With this analogy in mind, I turn to three papers, one written in 1976, one in 2013, and another released this September.  In 2013, James Hansen and 17 other scientists published “Assessing ‘Dangerous Climate Change’:  Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature.”( Dangerous climate change) Their paper documented the continued rise in atmospheric carbon dioxide from fossil fuel combustion, along with the various attendant impacts to Earth system processes, the environment and human health and well-being arising from this accumulation.  The authors suggested that the inertia of the climate system causes it to respond “slowly to this man-made forcing,” complicating policy responses, as well as obscuring the potentiality for irreversible climate change due to slow feedbacks.  Although the rapidity and scale of such changes; e.g., irreversible melting of Antarctic and/or Greenland ice sheets remains unclear, continued combustion of fossil fuels threatens to lock us into this future. 

They argued that the implications of future climate change already “in the pipeline” are thus intergenerational, presenting young people of today with a future they will have had no hand in shaping.  The authors suggested that “(a) scenario is conceivable in which growing evidence of climate change and recognition of implications for young people lead to massive public support for action” based on the expectation of “fairness and justice in a matter as essential as the condition of the planet they will inhabit.” This sounds remarkably like the argument underlying today’s campaign by young people for climate justice. The conclusions of the 2013 paper are stark:  the opportunity to avoid climate disruptions and maintain global temperatures below 2oC will require “extraordinarily rapid emission reductions” and choosing an alternative energy pathway, a “fork in the road” from a carbon-rich energy path to one that is carbon-free.   

The choice of a “hard energy path” as opposed to a “soft energy path” was outlined more than forty years ago, in Amory Lovin’s seminal October 1976 Foreign Affairs article “Energy Strategy:  The Road Not Taken?” (Soft Energy Paths) in which he outlined the numerous benefits of shifting from a “hard path” of fossil fuels and nuclear power to a “soft path” of efficiency and renewable energy, focused on matching the quality of energy to its end use.  Lovins’ deeply controversial and influential article showed a way forward to an energy future that today bears a remarkable similarity to his original description.  However, despite rapid efficiency improvements, technological breakthroughs and movement along a soft energy path envisioned by Lovins, a key aspect of the soft energy path, deployment of renewables, lags approximately 25 years behind the 1976 projections.  Deployment of renewables must therefore accelerate even more rapidly if we are to move towards an energy future that will avoid the irreversible climate change outlined by Hansen et al.

These choices are now before us, laid out in a September 2019 White Paper from the World Economic Forum, “The Speed of the Energy Transition—Gradual or Rapid Change?”  (The speed of the energy transition) The paper poses the question “Will the global energy transition from fossil fuels to sustainable energy be gradual or rapid?”  The authors suggest the choice of paths will be made this decade, that the two paths are mutually exclusive, and that the choice of business as usual “regrettably … means that the goals of the Paris Agreement will become increasingly unachievable.” 

There are three “signposts” along the path to a Rapid global energy transition by 2030 according to the White Paper: 

(1)  solar electricity at $20-$30 per megawatt hour

(2)  carbon taxes implemented on around half of emissions at $20 per tonne

(3)  three peaks to take place in the 2020’s

            a.  peak demand for new internal combustion engine cars

            b.  peak demand for fossil fuels in electricity

            c.  peak demand for all fossil fuels

If we pass these, the Rapid transition is on track; failure to pass these leads to a future whose socioeconomic  and Earth system dimensions will be dictated by processes humanity has set into irreversible motion.  The chart from Hansen, et al hints at the potential long lags in the climate system’s response to fossil fuel emission cuts: it could take centuries before atmospheric carbon dioxide levels return to “safe” levels of 350 ppm.  

Carbon dioxide has a long residence time in the atmosphere; the longer we delay in cutting emissions, the longer it will take for CO2 to return to “safe” levels after we reduce emissions. From Hansen, et al., 2013 (See link in the article)

The chart below from BerkelyEarth shows the path to 1.5oC is only a decade or so distant, if current trends continue.  The chart shows a ten-year moving average of the Earth’s surface temperature, plotted relative to the average temperature from 1850-1900.  At the current rate of increase, 1.5oC above the 1850-1900 average will be reached by 2035. 

Projected temperature increase if current trends continue
Source: BerkeleyEarth

According to Hansen et al., warming will reach 1.5oC and “stay above 1.0oC until 2400 if emissions continue to increase until 2030.”

Perhaps Greta Thunberg said it best in her September 23 address to the United Nations:

“For more than 30 years, the science has been crystal clear. How dare you continue to look away and come here saying that you’re doing enough, when the politics and solutions needed are still nowhere in sight…The popular idea of cutting our emissions in half in 10 years only gives us a 50% chance of staying below 1.5 degrees [Celsius], and the risk of setting off irreversible chain reactions beyond human control…Fifty percent may be acceptable to you. But those numbers do not include tipping points, most feedback loops, additional warming hidden by toxic air pollution or the aspects of equity and climate justice…You are failing us. But the young people are starting to understand your betrayal. The eyes of all future generations are upon you. And if you choose to fail us, I say: We will never forgive you. 

We will not let you get away with this. Right here, right now is where we draw the line. The world is waking up. And change is coming, whether you like it or not.” (Thunberg Transcript)

Image: Jon Tyson on Unsplash

July was hot!

Widespread heat set record temps globally

July was remarkably warm, in fact July’s average temperatures—for both land and sea–were the highest monthly temperatures ever recorded since 1850.  This image from NOAA illustrates some of the more noteworthy records set last month.


Source:  https://www.ncdc.noaa.gov/sotc/global/201907

I should also mention that Berkeley Earth (http://berkeleyearth.org), in their summary of 2018 global temperatures published early this year, estimated that 2019 would “…likely… be warmer than 2018, but unlikely to be warmer than the current record year, 2016.  At present it appears that there is roughly a 50% likelihood that 2019 will become the 2nd warmest years since 1850.” As of August 15, they are now predicting a 90% probability of this occurring.   This screenshot from Robert Rohde’s (BerkeleyEarth) Twitter feed illustrates long-term weather stations (those with at least 40 years of records) that have reported a daily, monthly or all-time record high temperature from May 1st to July 31st.  Looks like a sea of red!

Screenshot, August 19 @RARohde

Some of the more attention-grabbing aspects of the late July heat wave came from Greenland.

Warm air masses from Europe arrived over Greenland late in July and early August, causing record-setting melting across about 90% of the ice sheet during a five-day event.  Melt area reached 154,500 square miles, 18% larger than the 1988-2017 average. The record warmth established an all-time high melt event for this monthly period, and total ice mass loss for 2019 is nearly equal to that of 2012, the year of highest loss for the satellite-era.  (National Snow and Ice Data Center Greenland Today)

It’s not all about the records!

Considerable attention has been given to elevated Arctic temperatures, increased ice-sheet melt and its contributions to sea-level rise,  and low seasonal sea-ice coverage, but several other issues attending warming air and sea temperatures warrant discussion as well.   Over the longer term—decades, not days, warming temperatures are measurably impacting terrestrial and marine ecosystems.  These “slow” ecosystem changes aren’t as attention-grabbing as all-time records of high temperature or ice melt, but are one of the distinguishing characteristics of the Anthropocene. (see “The Anthropocene” tab on the Home page).  Let’s look at a couple of examples, one from terrestrial ecosystems, and one from marine ecosystems. 

In a July 10 article (Hydrologic Intensity) the authors demonstrate in a more complete fashion than previous work, the linkage between rising air temperatures and acceleration of the hydrological cycle.  Their model incorporates both the supply of water (precipitation) and demand (evapotranspiration) between the surface and the atmosphere.  Reinforcing other research that suggests hydrologic intensification is occurring, the new research shows “widespread hydrologic intenstification from 1979-2017 across much of the global land surface, which is expected to continue into the future.”  The findings add a little more support to the likelihood of a climate future where there is “increased precipitation intensity along with more days with low precipitation.”  The temporal and spatial distribution of hydrologic intensification will have important consequences ranging from urban flood control to the management of  agroecosystems—an issue of considerable importance as population rises this century. 

Marine fisheries are also significant food sources for global populations.  In an article published in March (Science https://science.sciencemag.org/content/363/6430/979) researchers looked at 235 marine fisheries (fish and invertebrates) from 38 ecoregions, representing one-third of reported global catch.   They  concluded that there has been a statistically significant decline in the maximum sustainable yield of 4.1% from 1930 to 2010 that is linked to warming oceans. Five of the ecoregions had losses of 15 to 35%. The authors conclude that “ocean warming has driven declines in marine fisheries productivity and the potential for sustainable fisheries catches.”  These trends are exacerbated by overfishing, but sound management plans incorporating temperature-driven trends have the potential for remediating these changes. 

Both examples suggest that temperature-driven changes to key provisioning services of  terrestrial and marine ecosystems are of equal importance to the headline-grabbing temperature and ice-melt records of the last month.  These changes are “slow-motion” impacts of a warming world; like rising sea-levels, ecosystem changes will have profound impacts, but are invisible over short-term news and policy cycles in which we appear to be ensnared.   

Blog Image Source: https://earthobservatory.nasa.gov/images/145377/a-second-scorching-heatwave-in-europe

More veggies, less meat to help save forests and climate

The recently (Aug 7) released Special Report on Climate Change and Land by the IPCC (https://www.ipcc.ch/srccl-report-download-page/) offers a comprehensive review of the nexus between global warming/climate change and land use change.  As I have already suggested in the “About this blog,” land use changes are a critical aspect of global anthropogenic change; i.e. the Anthropocene. The new report stresses how a changing climate (increased air temperatures, evapotranspiration, altered precipitation regimes, etc.) impact soils and vegetation.  The latter underlie ecosystem health, including agroecosystems, as well as intact “undisturbed” terrestrial ecosystems such as rainforests, peatland, and coastal forests.  These are critical harbors of biodiversity, as well as essential elements in the provision of ecosystem services upon which human well-being depends, such as carbon sequestration and clean water. 

Land use changes associated with agriculture, forestry, livestock, road construction, and urbanization degrade these critical services, thereby threatening our ability to sustainably provide food, fiber and other essential goods and services to a continually growing, telecoupled global population.  Imprudent and ill-planned (or adhoc) conversion of various terrestrial ecosystems in pursuit of food, fiber and mineral resources has led to land degradation, desertification and biodiversity loss at both a scale and speed that are without precedent.

The report emphasizes the urgent need to rein in these unsustainable practices in order to both guarantee our ability to provide food for the world, as well as provide a crucial sink for growing carbon emissions.  According to the report, reducing forest deforestation and degradation are critical elements in mitigating green house gas emissions.  Furthermore, transitioning the global population to a much more plant-based diet from one that is significantly animal-sourced, will reduce risks from climate change as well as help reduce agricultural extensification. 

Only a wide-ranging and comprehensive approach to managing both our energy and land resources will provide sustainable, equitable and healthy outcomes for the global population.  Immediate steps need to be taken, because the longer business as usual behaviors continue, our ability to deploy a wide variety of remedies will be increasingly foreclosed.  Reducing green house emissions and altering detrimental land use practices are thus interconnected, inseparable and our failure to change both may lead to both irremediable impacts to ecosystems and the goods and services upon which humanity relies.

Image: Photo by Tobias Quartey on Unsplash https://unsplash.com/photos/v55hpwzuZmI

Sea Level Rise

Photo by Mink Mingle on Unsplash
           
  • February 2019:  91 (+/- 4mm)  (Data since January 1, 1993)
  • Current Rate of Change:  +3.3 mm/year
    • 20th century average:  1.7 mm/year
  • Sources of sea level rise in the last decade
    • Endorheic global decline
    • 65%-85% due to thermal expansion (~1.1-1.4mm/yr)
    • Greenland, Antarctica ice sheet mass loss (~1.1-1.3mm/yr)
    • ~20-35% from other sources including mountain glacier and ice-cap loss, groundwater depletion, reservoir impoundment, and mass changes in other stores; e.g., lakes, soil, permafrost
    • the cumulative global groundwater depletion from 1900–2008 totaled ∼4,500 km3 from 1900–2008, equivalent to a sea‐level rise of 12.6 mm. As an identifiable, separate, semi‐independent hydrologic process, the volume and rate of estimated long‐term global groundwater depletion balances 6 to 7 percent of the observed SLR since 1900. (Konikow LF (2011) Contribution of global groundwater depletion since 1900 to sea-level rise. Geophys Res Lett 38(17), L17401. doi: 10.1029/2011gl048604)

Sea level rise is due to thermal expansion of seawater as it accumulates heat (see         above) and additional water from melting ice sheets and glaciers.

  Observed sea level since the start of the satellite altimeter record in 1993 (black line), plus independent estimates of the different contributions to sea level rise: thermal expansion (red) and added water, mostly due to glacier melt (blue). Added together (purple line), these separate estimates match the observed sea level very well. NOAA Climate.gov graphic, adapted from Figure 3.15a in State of the Climate in 2017.

Sea Level Tracked By Satellite Data 1993-Present


Source:  NASA Sea Level

Sea Level Derived From Coastal Tide Gauge Data 1870-2000


Source:  NASA Sea Level

               

Climate Change: Cryosphere


Greenland Ocean Sunset  Photo by William Bossen on Unsplash

Arctic Regions: Permafrost, Sea Ice

Permafrost

Over the 1900 to present time span roughly 4.5 Million sq km of potential permafrost area has been lost. Berkeley Earth Permafrost


Map of estimated 0 to 3 m deep carbon inventory stored in the circum-Arctic permafrost region (Hugelius et al., 2014Kanevskiy et al., 2011Romanovskii, 1993). The eastern boundary of Canadian Yedoma areas is uncertain, indicated as a dotted line at the Alaskan/Yukon state border. The conceptual permafrost carbon climate feedback cycle is illustrated in the middle. The Yedoma domain marks the potential maximum occurrence of widespread Yedoma deposits but also includes other deposits that formed after degradation of Yedoma, such as thermokarst deposits. In West Siberia and the Russian Far East Yedoma occurs sporadically, e.g. in river valleys. (Deep Yedoma permafrost)

(Permafrost Carbon Network); Global carbon storage in soils and atmospheric carbon

Significance:  Approximately 1330-1580 Pg of soil carbon are estimated  to be stored in soils and permafrost of high latitude ecosystems, which is almost twice as much carbon as is currently contained in the atmosphere. In a warmer world permafrost thawing and decomposition of previously frozen organic carbon is one of the more likely positive feedbacks from terrestrial ecosystems to the atmosphere. Although ground temperature increases in permafrost regions are well documented there is a knowledge gap in the response of    permafrost carbon to climate change. (Permafrost Carbon Network)

Total estimated carbon storage is ~1300 Pg with an uncertainty range of between 1100 and 1500 Pg. Around 800 Pg carbon is perennially frozen, equivalent to all carbon dioxide currently in the Earth’s atmosphere. (Permafrost Carbon)


Global carbon storage in soils and atmospheric carbon

Permafrost potential is declining…


This figure shows the decline in permafrost potential over the 1850 to 2013 time period. The permafrost potential is defined by the decadal air temperature. If the annual average temperature over a 10 year period is 0C or below, then that area was regarded as permafrost. Over the 1900 to present time span roughly 4.5 Million sq km of potential permafrost area has been lost. Berkeley Earth Permafrost

Arctic Sea Ice

Average September (summer minimum) Extent Declining at -12.8%/decade (relative to 1981-2000 average

Ice Sheets: Antarctica, Greenland, The Third Pole

An ice sheet is a mass of glacial land ice extending more than 50,000 square kilometers (20,000 square miles). The two ice sheets on Earth today cover most of Greenland and Antarctica. During the last ice age, ice sheets also covered much of North America and Scandinavia.

Together, the Antarctic and Greenland ice sheets contain more than 99 percent of the freshwater ice on Earth. The Antarctic Ice Sheet extends almost 14 million square kilometers (5.4 million square miles), roughly the area of the contiguous United States and Mexico combined. The Antarctic Ice Sheet contains 30 million cubic kilometers (7.2 million cubic miles) of ice. TheGreenland Ice Sheet extends about 1.7 million square kilometers (656,000 square miles), covering most of the island of Greenland, three times the size of Texas.

Antarctica

-127.0 Gt per year +/- 39 (Mass variation since 2002)


Zodiac Cruising in Antarctica  Photo by James Eades on Unsplash
Ice mass measurements by NASA’s GRACE satellites

Source:  NASA Global Climate Change Ice Sheets

Elephant Island, Antarctica  Photo by Paul Carroll on Unsplash

Greenland

  • Greenland ice sheet is a major contributor to sea level rise, adding on average 0.47mm +/- 0.23 mm/year to global mean sea level between 1991 and 2015
  • The cryosphere as a whole has contributed around 45% of observed global sea level rise since 1993. 
  • Observations show surface lowering across virtually all regions of the ice sheet and at some locations up to -2.65m/year between 1995 and 2017

Overall Greenland has lost 255+/- 15 Gt/year of ice over the period 2003-2016, compared to a rate loss of 83 +/- 63 Gt/year in the 1993-2003 period. 

Narsarsuaq, Greenland
Photo by Mahlersilvan on Unsplash

Greenland ice mass loss and melt extent


(a) Mass change time series for the entire Greenland ice sheet generated by DTU (red) and TUDR (blue). (b) Ice mass trends for 2007–2011 provided by DTU (left) and TUDR (right).
(TUDR  Technische Universitat Dresden; DTU Technical University of Denmark)
Source:  Greenland Ice Sheet Mass Balance

Source:  NSIDC Greenland Today

Melting ice sheets contribute to sea level rise

Source:  Denmark Polar Portal

Mass Change and Contribution to sea level rise 2003-2016

The map shows the latest changes in mass derived from data from the GRACE satellites.  The graph show the gain in the mass of ice when there is precipitation, and how much of this mass is lost when snow and ice melt and when icebergs break off from the ice sheet’s major outlet glaciers. The difference in these mass changes over a glaciological year (September-August) is called the total mass balance of the Greenland Ice Sheet.

The graph illustrates the month-by-month development in changes of mass measured in gigatonnes, Gt (1 Gt is 1 billion tonnes or 1 km3 of water). The left axis on the graph shows how this ice mass loss corresponds to sea level rise contribution. 100 Gt corresponds to 0.28 mm global sea level rise).  All changes are given relative to June 2006.

Based on this data, it can be seen that during the period 2003-2011 the Greenland Ice Sheet has lost 234 km3 of water per year, corresponding to an annual contribution to the mean increase in sea level of 0.65 mm 

This data shows that most of the loss of ice occurs along the edge of the ice sheet, where independent observations also indicate that the ice is thinning, that the glacier fronts are retreating in fjords and on land, and that there is a greater degree of melting from the surface of the ice.  (See map)

High on the central region of the ice sheet, however, the GRACE satellites show that there is a small increase in the mass of the ice. Other measurements suggest that this is due to a small increase in precipitation/snowfall.  (See map)

The Third Pole (Hindu-Kush and the Tibetan Plateau) (Source:  Science magazine Acceleration of ice loss)


Drekong Monastery, Tibet Autonomous Region, China  Photo by Evgeny Nelmin on Unsplash

Significance: 

  • Contains the largest volume of freshwater outside of the polar regions.
  • One-seventh of the world’s population depends on rivers flowing from these mountains for water to drink and to irrigate crops
  • Average ice loss during 2000-2016 (-0.43 +/- 0.14 meters water equivalent/year) is double compared to 1975-2000 (-0.22 +/- 0.13 meters water equivalent)
  • Acceleration of mass loss is consistent with warming temperatures recorded by meterological stations in the region

Glacier Mass Balance

Source: (NOAA CLIMATE CHANGE GLACIER)


Glacier Bay, Alaska  Photo by Michael Denning on Unsplash

Significance:  Today, many glaciologists are more concerned with predicting when various glaciers will disappear. In many parts of the world—including the western United States, South America, China, and India—glaciers are frozen reservoirs that provide a reliable water supply each summer to hundreds of millions of people and the natural ecosystems on which they depend. NOAA CLIMATE CHANGE GLACIER

  • 2018:  -0.72 meters water equivalent*   World Glacier Monitoring Service
  • Among the most dramatic evidence that Earth’s climate is warming is the dwindling and disappearance of mountain glaciers around the world. Based on preliminary data, 2017 is likely to be the 38th year in a row of mass loss of mountain glaciers worldwide. According to the State of the Climate in 2017

The cumulative mass balance loss from 1980 to 2016 is -19.9 meters, the equivalent of cutting a 22-meter-thick (72-foot-thick) slice off the top of the average glacier.

The graph shows cumulative mass loss in “*meters of water equivalent,” which is the depth of the meltwater spread out over the glacier’s surface area.

Melting of mountain glaciers has accelerated since 2000

Glacier mass balance (gray bars) from 1980–2017 for 37 worldwide glaciers with at least a 30-year monitoring history. Observations for 2017 are preliminary. Cumulative mass losses (orange line) have accelerated since 2000. As of 2016, the total loss was -19.9 meters, the equivalent of cutting a 22-meter- (72-foot-) thick slice off the top of the average glacier. NOAA Climate.gov graph adapted from State of the Climate in 2017.

Mer de Glace, Chamonix, France
 
Photo by Martin Adams on Unsplash

Climate Change: Global Temperature

Visualizing Global Temperature Change:  “Small multiples” global temperature changes 1850-2017

–>
Mapping global temperature change 

Surface Air Temperature

  • 2018*:  +1.16oC (2.09oF) above 1850-1900 pre-industrial baseline average temperature
  • 4th warmest year on Earth since 1850
  • 6th warmest year in the Arctic
  • Global temperatures have risen at a rate of +0.19oC/decade (+0.34oF) since 1980
  • 1.5 oC will be reached by 2035 at current rates
  • Surface air temperatures in the Arctic continued to warm at twice the rate relative to the rest of the globe.
  • Arctic air temperatures for the last five years (2014-2018) have exceeded all previous records since 1900
  • Surface air temperatures in the Arctic continued to warm at twice the rate relative to the rest of the globe.
  • Arctic air temperatures for the last five years (2014-2018) have exceeded all previous records since 1900
  • Source: (NOAA Arctic)

*Source: Berkeley Earth Land+Ocean Dataset

Visualizing Global Temperature Change:  Ed Hawkins’ global temperature spiral


Click!  Global temperature change gif  (Ed Hawkins)

     

Agreement about the rise in global temperatures comes from multiple groups around the world…


Yearly global surface temperature from 1900–2017 compared to the 1981-2010 average (dashed line). The different colors represent different research groups’ analysis of the historical temperature record. NOAA Climate.gov graph adapted from State of the Climate in 2017Details on the datasets can be found in Table 2.1 and Figure 2.1 in the report.   Global Surface Temperature

Yearly global surface temperature from 1900–2017 compared to the 1981-2010 average (dashed line). The different colors represent different research groups’ analysis of the historical temperature record. NOAA Climate.gov graph adapted from State of the Climate in 2017. Details on the datasets can be found in Table 2.1 and Figure 2.1 in the report.  

Arctic Surface Air Temperatures (NOAA Arctic)

At +1.7° C, the mean annual surface air temperature (SAT) anomaly for October 2017-September 2018 for land stations north of 60° N is the second highest value (after 2016) in the record starting in 1900.  Currently, the Arctic is warming at more than twice the rate of global mean temperatures; a phenomenon known as Arctic Amplification.  Recorded annual mean Arctic temperatures over the past five years (2014-18) all exceed previous records.


Arctic (land stations north of 60° N) and global mean annual land surface air temperature (SAT) anomalies (in °C) for the period 1900-2018 relative to the 1981-2010 mean value.

It’s not just Berkeley Earth documenting global temperature…

Other scientific groups around the world document similar global temperature trends

      Global temperatures have been trending upwards, above the long-term average for more than 40 years.


The graph shows average annual global temperatures since 1880  (source data) compared to the long-term average (1901-2000). The zero line represents the long-term average temperature for the whole planet; blue and red bars show the difference above or below average for each year. NOAA Global Temperature Change

The period since 2015 has seen some of the warmest years since 1850. The probability distribution shown below clarifies this; note how 2016 was markedly warmer on average than earlier years.


Probability distribution on the mean temperature anomalies reveals 2015-2018 as a period of significant warmth well above all previous years since 1850.

Distribution of warming is uneven, but as in previous years, 2018 was characterized by very strong warming over the Arctic that significantly exceeds the Earth’s mean rate of warming.


44% of the Earth had “Very High” or higher temperatures in 2018.  If we lived in a world characterized by a stable climate, only 2.5% of the Earth would have been expected to have these temperatures.

Surface air temperature 2018:  Concurrent heat events (see

Source:  Vogel, M. M., Zscheischler, J., Wartenburger, R., Dee, D., & Seneviratne, S. I. (2019). Concurrent 2018 hot extremes across Northern Hemisphere due to human-induced climate change. Earth’s Future, 7. https://doi.org/10.1029/2019EF001189 (See table below)

  • Twenty-two percent of populated and agricultural areas of the Northern Hemisphere concurrently experienced hot extremes between May and July 2018 
  • Record-breaking temperatures occurred concurrently in multiple regions including North America, Europe, and Asia in late spring/summer 2018.
  •  Europe experienced late spring and summer temperatures that were more than 1◦C warmer than 1981–2010
  • The contiguous United States had the warmest May since 1895, and the hottest month ever observed was in July in Death Valley.
  • The 2018 hot temperatures are in line with an increase in intensity and frequency of extreme heat events over many regions on land and in the ocean in recent years.
  • It is virtually certain that these 2018 north hemispheric concurrent heat events could not have occurred without human-induced climate change
  • We would experience a GCWH18-like event* nearly 2 out of 3 years at +1.5 ◦C and every year at +2 ◦C global warming
  • Results further reveal that the average high-exposure area projected to experience concurrent warm and hot spells in the Northern Hemisphere increases by about 16% per additional +1 ◦C of global warming.

*the temporal average between May and July 2018 as considered Global Concurrent Warm and Hot 2018 event, in short, GCWH18 extreme event.


Approximate locations of heat-related impacts in the northern midlatitudes (above 30north).
The impacts are categorized according to heat impact (cross, purple text), fires (fire, red text), agricultural and ecological damages (wheat, orange text), damages to infrastructure (railway track, brown text), and impacts on power production reduction/shortage (warning signal, blue text).


Detailed heat-related impacts per country. The color refers to the categories in (a).  References for each heat-related impact and original table available at Vogel, et al.(see above)

Business As Usual Projections of Global Surface Temperature Will Push Global Temperatures Above 1.5 degrees C by 2035.


2 oC, often suggested as a risky,“next best” global temperature (2 degrees Celsius) will be reached by around 2060.