klimasensitiviteten - oversigt

Climate sensitivity refers to the amount of global surface warming that will occur in response to a doubling of atmospheric CO2 concentrations compared to pre-industrial levels.

There are three main measures of climate sensitivity that scientists use. The first is equilibrium climate sensitivity (ECS). The Earth's climate takes time to adjust to changes in CO2 concentration. For example, the extra heat trapped by a doubling of CO2 will take decades to disperse down through the deep ocean. ECS is the amount of warming that will occur once all these processes have reached equilibrium.

The second is transient climate response (TCR). This is the amount of warming that might occur at the time when CO2 doubles, having increased gradually by 1% each year. TCR more closely matches the way the CO2 concentration has changed in the past. It differs from ECS because the distribution of heat between the atmosphere and oceans will not yet have reached equilibrium.

A third way of looking at climate sensitivity, Earth system sensitivity (ESS), includes very long-term Earth system feedbacks, such as changes in ice sheets or changes in the distribution of vegetative cover.

TCR tends to be notably lower than ECS. The Intergovernmental Panel on Climate Change (IPCC) fifth assessment report, completed in 2014, gave a likely ECS range of 1.5C to 4.5C of warming for a doubling of atmospheric CO2 concentrations, but a likely TCR of only 1C to 2.5C.

CO2 has increased from its pre-industrial level of 280 parts per million (ppm) to around 408 ppm today. Without actions to reduce emissions concentrations are likely to reach 560 ppm – double pre-industrial levels – around the year 2060.

The wide range of estimates of climate sensitivity is driven by uncertainties in climate feedbacks, including how water vapour, clouds, surface reflectivity and other factors will change as the Earth warms. Climate feedbacks are processes that may amplify (positive feedbacks) or diminish (negative feedbacks) the effect of warming from increased CO2 concentrations or other climate forcings – factors that initially drive changes in the climate.

Simple physics shows the world will warm by a bit more than 1C once CO2 doubles, if feedbacks are not taken into account. However, there is extremely strong evidence that feedbacks will amplify this warming, based on the Earth's past and the physical processes involved.

Water vapour – itself a powerful greenhouse gas – is the single largest and one of the best-understood climate feedbacks. As the world warms, the amount of water vapour in the atmosphere is expected to increase and, therefore, so too will the greenhouse effect.

Measurements from satellites confirm that water vapour concentrations have been increasing in step with temperatures in the atmosphere over the past few decades.

A warmer and wetter atmosphere will also affect cloud cover. However, it is much more uncertain how changes in cloud cover will influence climate sensitivity.

An increase in low-altitude clouds would tend to offset some warming by reflecting more sunlight back to space, whereas an increase in the height of high-altitude clouds would trap extra heat. Meanwhile a shift in sun-blocking clouds from the tropics towards the poles, where the incoming sunlight is less intense, would decrease their power to block sunlight.

Changes in the composition of clouds also matter: clouds that contain more water droplets are "optically thicker" and more effective at blocking sunlight than those composed mainly of ice crystals. All this means the global net effect of cloud feedbacks is complex and hard for scientists to model precisely.

A warming world will also have less ice and snow cover. With less ice and snow reflecting the sun's rays, melting will decrease Earth's albedo and amplify warming.

The combination of these and other feedbacks converts the ~1C warming from doubled CO2 alone into an uncertain range of possible warming, from around 1.5C to 4.5C.

The combination of these and other feedbacks converts the ~1C warming from doubled CO2 alone into an uncertain range of possible warming, from around 1.5C to 4.5C

Kjeld Jul skrev:
Ja lad os tærske mere langhalm.
Vi anvender TCR.
Opvarmning fra 1979 til 2018 er 0,60K
Det svarer til en temperatur på 2,1K ved en fordobling af CO2 fra 280 til 560 ppm.

Niels K Sørensen skrev:

Kjeld Jul skrev:
Ja lad os tærske mere langhalm.
Vi anvender TCR.
Opvarmning fra 1979 til 2018 er 0,60K
Det svarer til en temperatur på 2,1K ved en fordobling af CO2 fra 280 til 560 ppm.

Sludder og vrøvl.

Primitive forenklinger på komplekse problemstillinger er nonsens.
Læs og forstå artiklen, der er ikke grund til at kommentere, når ikke det tilføjer noget ny information.
Mvh Niels

Charney Report
In 1979 Charney chaired an "ad hoc study group on carbon dioxide and climate" for the National Research Council. The resulting 22-page report, "Carbon dioxide and climate: A scientific assessment", is one of the earliest modern scientific assessments about global warming. Its main conclusion can be found on page 2: "We estimate the most probable global warming for a doubling of CO2 to be near 3°C with a probable error of ± 1.5°C." This estimate of climate sensitivity has been essentially unchanged for over three decades, e.g., the IPCC Fourth Assessment Report (2007) says that "equilibrium climate sensitivity is likely to be in the range 2°C to 4.5°C, with a best estimate value of about 3°C. It is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement with observations is not as good for those values."

Niels K Sørensen skrev:

Charney Report
In 1979 Charney chaired an "ad hoc study group on carbon dioxide and climate" for the National Research Council. The resulting 22-page report, "Carbon dioxide and climate: A scientific assessment", is one of the earliest modern scientific assessments about global warming. Its main conclusion can be found on page 2: "We estimate the most probable global warming for a doubling of CO2 to be near 3°C with a probable error of ± 1.5°C." This estimate of climate sensitivity has been essentially unchanged for over three decades, e.g., the IPCC Fourth Assessment Report (2007) says that "equilibrium climate sensitivity is likely to be in the range 2°C to 4.5°C, with a best estimate value of about 3°C. It is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement with observations is not as good for those values."

Charney døde i 1981.

Jeg vil her sige tak for dine kommentarer, jeg har ikke yderligere.
mvh Niels

Jørgen Petersen skrev:
Den fremsatte graf viser helt klart, at estimaterne over klimasensitivitet er blevet sat ned igennem de sidste 15 år. Det kan man ganske enkelt ikke bortforklare.

Niels K Sørensen skrev:
Seite nicht gefunden.
Er det svært at kopiere et link ind?
Brug dog URL omkring link, og check dem selv inden du poster dem.
Mvh Niels

Kjeld Jul skrev:
Jørgen-
Man kan ved st bruge den empiriske formel for Ts og indsættelse af CO2 få en indikator for en reducering af klimasensiviteten.
Temperaturstigningen fra 1979 til 2010 var 0,49 K det svarede til 2,3 K ved en fordobling af CO2.
Temperaturstigningen fra 1979 til 2018 er o,60 K, det svarer til 2.1 K ved en fordobling, dvs klimasensiviteten er blevet mindre på 8 år.
Det er kun en simpel beregning, , men et tegn på at sensiviteten er blevet mindre.

Kjeld Jul skrev:

Niels K Sørensen skrev:
Seite nicht gefunden.
Er det svært at kopiere et link ind?
Brug dog URL omkring link, og check dem selv inden du poster dem.
Mvh Niels

Beklager - der havde indsneget sig en tastefejl - skulle stå " klimasensivitaet".
Heldigvis havde k - v fanget féjlen.
Mvh
Kjeld

Niels K Sørensen skrev:
Kan du overhovedet finde et eneste forskningsinstitut, der påstår lavere klimasensitivitet gennem videnskabeligt assessment end 3 +/- 1,5 grader.
Svaret er NEJ.
Det findes ikke - jeg har intet seriøst kunnet finde.
Mvh Niels

Kjeld Jul skrev:
Iflg. NATURE er der en tendens til en mindre klimasensitivitet.

https://www.nature.com/articles/nature25450

Kjeld Jul skrev:
Faktuel:
Fra 1979 til idag er den globale temperatur steget med 0,60 C ,det svarer til 2,1 C ved en fordobling af CO2 fra 280 til 560 ppm.

Der er lavet så mange divergerende prognoser over den fremtidige temperatur og klimasensitiviteten ,at alle udmeldinger skal tages med det største forbehold.

Kjeld Jul skrev:
Hvis vi leger med tallene,
Fra 1979 til 2018 er CO2 indholdet steget fra 336 til 410 ppm = 74 ppm, eller ca. 1,9 ppm /år.
Fortsætter denne trend vil der være ca. 560 ppm i år 2100, ca en fordobling i forh. til det preindustrielle eller svarende til ca. + 2,1 C i forhold til den gang
Dette estimat kan være ligeså rigtig som andre prognoser
Nogle forskere regner jo med at temperaturen over de næste årtier vil falde med omk. 0,1 C pga. af Solens aftagende aktivitet,så denne antagelse skal også indregnes.

Estimating the equilibrium climate sensitivity (ECS; the equilibrium warming in response to a doubling of CO2) from observations is one of the big problems in climate science. Using observations of interannual climate variations covering the period 2000 to 2017, we estimate ECS is likely 2.4-4.5 K (17-83% confidence interval), with a mode and median value of 2.9 and 3.3 K, respectively. Our analysis provides no support for low values of ECS (below 2 K) suggested by other analyses. The main uncertainty in our estimate is not observational uncertainty, but rather uncertainty in converting observations of short-term, mainly unforced climate variability to an estimate of the response of the climate system to long-term forced warming.

NCA4 rapport: Global climate is projected to continue to change over this century and beyond. The magnitude of climate change beyond the next few decades will depend primarily on the amount of greenhouse (heat-trapping) gases emitted globally and on the remaining uncertainty in the sensitivity of Earth's climate to those emissions (very high confidence). With significant reductions in the emissions of greenhouse gases, the global annually averaged temperature rise could be limited to 3.6°F (2°C) or less.
Without major reductions in these emissions, the increase in annual average global temperatures relative to preindustrial times could reach 9°F (5°C) or more by the end of this century (high confidence).

Videre fra NCA4 rapport: Global climate is projected to continue to change over this century and beyond. The magnitude of climate change beyond the next few decades will depend primarily on the amount of greenhouse (heat-trapping) gases emitted globally and on the remaining uncertainty
in the sensitivity of Earth's climate to those emissions (very high confidence). With significant reductions in the emissions of greenhouse gases, the global annually averaged temperature rise could be limited to 3.6°F (2°C)
or less. Without major reductions in these emissions, the increase in annual average global temperatures relative to preindustrial times could reach 9°F (5°C) or more by the end of this century (high confidence).

Kjeld Jul skrev:
Niels-
Det kommer helt an på.ENSO udviklingen og andre feedbacks, hvordan temperaturen/ klimasensitiviteten bliver, prognoseusikkerheden afspejler sig jo klart i IPCCs estimat ,3 +÷ 1,5 C.