Global Warming Opens Up Antarctic Waterways

[jackdale]

Originally Posted by SV THIRD DAY

She's an engineer....you are a...???

Then she should be able to get her variables correct.

[tp12]

Originally Posted by Reefmagnet

Yep, I'm definitely the troll.


Sent from my SGP521 using Cruisers Sailing Forum mobile app

Umm, did you actually read your post? Seriously, you've proven my point.

You make a comment regarding a weather extreme being attributed to global warming in your post and that's not provocative? Despite the well known fact that climate change means that some places will face weather extremes of cold as well as hot ... And you call my response to that out as trolling? HAHAHAHAHAHAHAHAHAHA You are a crack up

Maybe quit while you're behind?

[sailorchic34]

Originally Posted by jackdale

Then she should be able to get her variables correct.

Honey, My numbers are as good as your numbers. I actually calculated some of mine or double checked some. If you look at your bar graph, notice the error bars, those little black lines that give the +/- error range of where the data point may actually lay.. The data point is somewhere within the error range, this as they are calculating based on statistics, not on hard numbers

So while the graph shows a 1.6 ish watt/m2 for co2, the low error range is 1.3, for that model. Other models use different numbers. I used 1.2 watt/m2 for CO2 which is in the ball park of co2 forcing and is a number I read somewhere, perhaps in a IPCC report.

The 11 year solar cycle varies by 1.3 watt's per m2. That's actually measured over the last three solar cycles. Here is the link Solar variation - Wikipedia, the free encyclopedia

Oddly the solar variation over the last 1000 years closely follows temperature. How odd.

So Solar forcing does vary just about as much as CO2 forcing. To say that solar and orbital dynamics does not play a role in the earths climate is pretty much like saying that the ice ages were caused by AGW. We started coming out of the little ice age ( Maunder Minimum) back in 1750's and the earth has been more or less warming ever since.

[Eumelia]

By far the main cause of global warming is surely the sun, for which I am very thankful

Sent from my LG-D415 using Cruisers Sailing Forum mobile app

[jackdale]

Originally Posted by sailorchic34

I used 1.2 watt/m2 for CO2 which is in the ball park of co2 forcing and is a number I read somewhere, perhaps in a IPCC report.

From AR5

AR4 gives
an 11-year running mean instantaneous TOA RF between 1750 and
the present of 0.12 W m–2 with a range of estimates of 0.06 to 0.30 W
m–2, equivalent to a RF of 0.09 W m–2 with a range of 0.05 to 0.23 W
m–2.

CO2 RF 1.82 ± 0.19

https://www.ipcc.ch/pdf/assessment-r...er08_FINAL.pdf

CO2 RF is at least 10 times higher.

Which is consistent with:

Cosmic rays, solar activity and the climate

OPEN ACCESS FOCUS ON HIGH ENERGY PARTICLES AND ATMOSPHERIC PROCESSES

T Sloan and A W Wolfendale 2013 Environ. Res. Lett. 8 045022
doi:10.1088/1748-9326/8/4/045022

Abstract
Although it is generally believed that the increase in the mean global surface temperature since industrialization is caused by the increase in green house gases in the atmosphere, some people cite solar activity, either directly or through its effect on cosmic rays, as an underestimated contributor to such global warming. In this letter a simplified version of the standard picture of the role of greenhouse gases in causing the global warming since industrialization is described. The conditions necessary for this picture to be wholly or partially wrong are then introduced. Evidence is presented from which the contributions of either cosmic rays or solar activity to this warming is deduced. <b>The contribution is shown to be less than 10% of the warming seen in the twentieth century.</b>

And

Small influence of solar variability on climate over the past millennium

Andrew P. Schurer, Simon F. B. Tett & Gabriele C. Hegerl

Nature Geoscience (2013) doi:10.1038/ngeo2040
Received 02 August 2013 Accepted 14 November 2013 Published online 22 December 2013

The climate of the past millennium was marked by substantial decadal and centennial scale variability in the Northern Hemisphere. Low solar activity has been linked to cooling during the Little Ice Age (AD 1450–1850; ref. 1) and there may have been solar forcing of regional warmth during the Medieval Climate Anomaly (AD 950–1250; ref. 1). The amplitude of the associated changes is, however, poorly constrained with estimates of solar forcing spanning almost an order of magnitude. Numerical simulations tentatively indicate that a small amplitude best agrees with available temperature reconstructions. Here we compare the climatic fingerprints of high and low solar forcing derived from model simulations with an ensemble of surface air temperature reconstructions for the past millennium. Our methodology also accounts for internal climate variability and other external drivers such as volcanic eruptions, as well as uncertainties in the proxy reconstructions and model output. We find that neither a high magnitude of solar forcing nor a strong climate effect of that forcing agree with the temperature reconstructions. We instead conclude that solar forcing probably had a minor effect on Northern Hemisphere climate over the past 1,000 years, while, volcanic eruptions and changes in greenhouse gas concentrations seem to be the most important influence over this period.

[jackdale]

Originally Posted by Eumelia

By far the main cause of global warming is surely the sun, for which I am very thankful

Sent from my LG-D415 using Cruisers Sailing Forum mobile app

The warmth comes from the sun, but it is not significant in climate change.

[SV THIRD DAY]

Religion....you are trying to tell a member of ISIS that Allah isn't god...once you understand who you are dealing with, you realize they are not dealing with logic, but with faith. Then you just laugh at them....tease them here and there and poke the dog...

[Hearts Content]

When you see incredible wealthy people supporting something in mass, you have to ask why. It's one of the greatest money scams in history and they want a part of it.

See that's how you get insanely wealthy.

Originally Posted by SailOar

Open Letter from Global CEOs to World Leaders Urging Concrete Climate Action

[SV THIRD DAY]

Two Words:
Carbon Credits

The amount of money the Carbon Traders will make trading a natural occurring plant food will make Big Oil's Profits look like a Joke. Follow the money my friends....

[tp12]

Originally Posted by SV THIRD DAY

Two Words:
Carbon Credits

The amount of money the Carbon Traders will make trading a natural occurring plant food will make Big Oil's Profits look like a Joke. Follow the money my friends....

That's redundant as there's money on both sides of the argument - big oil for example.

[sailorchic34]

Originally Posted by jackdale

The warmth comes from the sun, but it is not significant in climate change.

Does that not sound strange. The warmth comes from the sun but its not a factor in climate change.

So I am to believe that a 3 percent increase in co2, which is 0.0012% of the atmosphere (the MM portion), where total co2 makes up all of 0.04% of the atmosphere, causes excess warming. Sort of the tail wagging the dog. Actually the tip of the tail wagging the dog.

Yet a change of 1 watt/m2 or 0.1% of total solar flux (actually 1.3 w/m2 variation in 11 year solar cycle but I'm rounding down) increase in solar output (oddly documented btw) which represents 2.4x10^12 kw per hour, has no effect what so ever.

Sorry no I don't believe that solar forcing number of 0.05 watt/m2. That is bogus. I don't see water vapor in the IPCC either but then it's not MM so not included. Is it not odd that they included solar but not water vapor. No the stratosphere water vapor does not count as most water vapor is below 33,000 feet

[SailOar]

A Challenge From Climate Change Regulations | New York Times

This summer, the Environmental Protection Agency is expected to release a final set of rules aimed at forcing electric power companies — the nation’s largest source of greenhouse gas emissions — to cut them 30 percent from 2005 levels by 2030. The Obama administration has consistently used 2005 as a baseline year for cutting greenhouse gas emissions.

The ambitious rules hope to remake the nation’s electricity system by closing hundreds of heavily polluting coal plants while rapidly expanding the use of natural gas plants, wind and solar power. Officials at electric utilities say that as they make that transition — taking the nation’s largest but dirtiest source of electricity offline and replacing it with a mix of cleaner power sources — they may face power failures.

“If the proposed rule stands the way it is, there will be blackouts,” said Nick Akins, the chief executive of American Electric Power, an electric utility that supplies power in 11 Midwestern states....

In the long run, Mr. Akins and officials from other electric utilities say that they do expect to meet the requirements of the regulation by 2030. The hard part, they say, will be maintaining reliable power during the transition. In particular, they note that the E.P.A.’s draft proposal requires states to start demonstrating significant emissions cuts as early as 2020.

“This is going to be a major transition of the electricity system. All these things can be done, but not in that time range,” said Gerry Cauley, president of the North American Electric Reliability Corporation....

“There is no way that E.P.A. is going to finalize this rule without being assured that the system will be reliable and cost-effective,” said Gina McCarthy, the E.P.A. administrator. “We are working with utilities on what needs to be tweaked.”

A report issued in February by the Analysis Group, a consulting firm based in Boston, concluded that there were ways for states to avoid blackouts and brownouts during the power transition. The report found, if states were to adopt interstate cap-and-trade plans, along the lines of the program in place in California, they could cut pollution while keeping the lights on....

[SailOar]

Originally Posted by sailorchic34

Does that not sound strange. The warmth comes from the sun but its not a factor in climate change.

So I am to believe that a 3 percent increase in co2, which is 0.0012% of the atmosphere (the MM portion), where total co2 makes up all of 0.04% of the atmosphere, causes excess warming. Sort of the tail wagging the dog. Actually the tip of the tail wagging the dog.

Yet a change of 1 watt/m2 or 0.1% of total solar flux (actually 1.3 w/m2 variation in 11 year solar cycle but I'm rounding down) increase in solar output (oddly documented btw) which represents 2.4x10^12 kw per hour, has no effect what so ever.

Sorry no I don't believe that solar forcing number of 0.05 watt/m2. That is bogus. I don't see water vapor in the IPCC either but then it's not MM so not included. Is it not odd that they included solar but not water vapor. No the stratosphere water vapor does not count as most water vapor is below 33,000 feet

How do human CO2 emissions compare to natural CO2 emissions?

Climate Myth...

Human CO2 is a tiny % of CO2 emissions
“The oceans contain 37,400 billion tons (GT) of suspended carbon, land biomass has 2000-3000 GT. The atpmosphere contains 720 billion tons of CO2 and humans contribute only 6 GT additional load on this balance. The oceans, land and atpmosphere exchange CO2 continuously so the additional load by humans is incredibly small. A small shift in the balance between oceans and air would cause a CO2 much more severe rise than anything we could produce.” (Jeff Id)


What the science says...

Manmade CO2 emissions are much smaller than natural emissions. Consumption of vegetation by animals & microbes accounts for about 220 gigatonnes of CO2 per year. Respiration by vegetation emits around 220 gigatonnes. The ocean releases about 332 gigatonnes. In contrast, when you combine the effect of fossil fuel burning and changes in land use, human CO2 emissions are only around 29 gigatonnes per year. However, natural CO2 emissions (from the ocean and vegetation) are balanced by natural absorptions (again by the ocean and vegetation). Land plants absorb about 450 gigatonnes of CO2 per year and the ocean absorbs about 338 gigatonnes. This keeps atmospheric CO2 levels in rough balance. Human CO2 emissions upsets the natural balance.


Figure 1: Global carbon cycle. Numbers represent flux of carbon dioxide in gigatonnes (Source: Figure 7.3, IPCC AR4).

About 40% of human CO2 emissions are being absorbed, mostly by vegetation and the oceans. The rest remains in the atmosphere. As a consequence, atmospheric CO2 is at its highest level in 15 to 20 million years (Tripati 2009). A natural change of 100ppm normally takes 5,000 to 20.000 years. The recent increase of 100ppm has taken just 120 years.

Additional confirmation that rising CO2 levels are due to human activity comes from examining the ratio of carbon isotopes (eg ? carbon atoms with differing numbers of neutrons) found in the atmosphere. Carbon 12 has 6 neutrons, carbon 13 has 7 neutrons. Plants have a lower C13/C12 ratio than in the atmosphere. If rising atmospheric CO2 comes from fossil fuels, the C13/C12 should be falling. Indeed this is what is occurring (Ghosh 2003). The C13/C12 ratio correlates with the trend in global emissions.


Figure 2: Annual global CO2 emissions from fossil fuel burning and cement manufacture in GtC yr?1 (black), annual averages of the 13C/12C ratio measured in atmospheric CO2 at Mauna Loa from 1981 to 2002 (red). ). The isotope data are expressed as ?13C(CO2) ‰ (per mil) deviation from a calibration standard. Note that this scale is inverted to improve clarity. (IPCC AR4)

[sailorchic34]

I can play that game too!

Link:THE HOCKEY SCHTICK: Climate scientist Dr. Murry Salby explains why man-made CO2 does not drive climate change

Climate scientist Dr. Murry Salby explains why man-made CO2 does not drive climate change


Climate scientist Dr. Murry Salby, Professor and Climate Chair at Macquarie University, Australia explains in a recent, highly-recommended lecture presented at Helmut Schmidt University, Hamburg, Germany, why man-made CO2 is not the driver of atmospheric CO2 or climate change. Dr. Salby demonstrates:

• CO2 lags temperature on both short [~1-2 year] and long [~1000 year] time scales
• The IPCC claim that "All of the increases [in CO2 concentrations since pre-industrial times] are caused by human activity" is impossible
• "Man-made emissions of CO2 are clearly not the source of atmospheric CO2 levels"

• Satellite observations show the highest levels of CO2 are present over non-industrialized regions, e.g. the Amazon, not over industrialized regions
• 96% of CO2 emissions are from natural sources, only 4% is man-made
• Net global emissions from all sources correlate almost perfectly with short-term temperature changes [R2=.93] rather than man-made emissions
• Methane levels are also controlled by temperature, not man-made emissions
• Climate model predictions track only a single independent variable - CO2 - and disregard all the other, much more important independent variables including clouds and water vapor.
• The 1% of the global energy budget controlled by CO2 cannot wag the other 99%
• Climate models have been falsified by observations over the past 15+ years
• Climate models have no predictive value
• Feynman's quote "

  It doesn’t matter how beautiful your theory is, it doesn’t matter how smart you are. If it doesn’t agree with the data, it’s wrong" applies to the theory of man-made global warming.

[SailOar]

Originally Posted by sailorchic34

Does that not sound strange. The warmth comes from the sun but its not a factor in climate change.

So I am to believe that a 3 percent increase in co2, which is 0.0012% of the atmosphere (the MM portion), where total co2 makes up all of 0.04% of the atmosphere, causes excess warming. Sort of the tail wagging the dog. Actually the tip of the tail wagging the dog.

Yet a change of 1 watt/m2 or 0.1% of total solar flux (actually 1.3 w/m2 variation in 11 year solar cycle but I'm rounding down) increase in solar output (oddly documented btw) which represents 2.4x10^12 kw per hour, has no effect what so ever.

Sorry no I don't believe that solar forcing number of 0.05 watt/m2. That is bogus. I don't see water vapor in the IPCC either but then it's not MM so not included. Is it not odd that they included solar but not water vapor. No the stratosphere water vapor does not count as most water vapor is below 33,000 feet

How sensitive is our climate?

Some global warming 'skeptics' argue that the Earth's climate sensitivity is so low that a doubling of atmospheric CO2 will result in a surface temperature change on the order of 1°C or less, and that therefore global warming is nothing to worry about. However, values this low are inconsistent with numerous studies using a wide variety of methods, including (i) paleoclimate data, (ii) recent empirical data, and (iii) generally accepted climate models.

^^^^^^^^^^^^^^^

Climate sensitivity describes how sensitive the global climate is to a change in the amount of energy reaching the Earth's surface and lower atmosphere (a.k.a. a radiative forcing). For example, we know that if the amount of carbon dioxide (CO2) in the Earth's atmosphere doubles from the pre-industrial level of 280 parts per million by volume (ppmv) to 560 ppmv, this will cause an energy imbalance by trapping more outgoing thermal radiation in the atmosphere, enough to directly warm the surface approximately 1.2°C. However, this doesn't account for feedbacks, for example ice melting and making the planet less reflective, and the warmer atmosphere holding more water vapor (another greenhouse gas).

Climate sensitivity is the amount the planet will warm when accounting for the various feedbacks affecting the global climate. The relevant formula is:
dT = λ*dF
Where 'dT' is the change in the Earth's average surface temperature, 'λ' is the climate sensitivity, usually with units in Kelvin or degrees Celsius per Watts per square meter (°C/[W m-2]), and 'dF' is the radiative forcing, which is discussed in further detail in the Advanced rebuttal to the 'CO2 effect is weak' argument.

Climate sensitivity is not specific to CO2
It's important to note that the surface temperature change is proportional to the sensitivity and radiative forcing (in W m-2), regardless of the source of the energy imbalance. The climate sensitivity to different radiative forcings differs depending on the efficacy of the forcing, but the climate is not significantly more sensitive to other radiative forcings besides greenhouse gases.

Figure 1: Efficacies of various radiative forcings as calculated in numerous different studies (IPCC 2007)

In other words, if you argue that the Earth has a low climate sensitivity to CO2, you are also arguing for a low climate sensitivity to other influences such as solar irradiance, orbital changes, and volcanic emissions. In fact, as shown in Figure 1, the climate is less sensitive to changes in solar activity than greenhouse gases. Thus when arguing for low climate sensitivity, it becomes difficult to explain past climate changes. For example, between glacial and interglacial periods, the planet's average temperature changes on the order of 6°C (more like 8-10°C in the Antarctic). If the climate sensitivity is low, for example due to increasing low-lying cloud cover reflecting more sunlight as a response to global warming, then how can these large past climate changes be explained?


Figure 2: Antarctic temperature changes over the past 450,000 years as measured from ice cores

What is the possible range of climate sensitivity?
The IPCC Fourth Assessment Report summarized climate sensitivity as "likely to be in the range 2 to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement of models with observations is not as good for those values."

Individual studies have put climate sensitivity from a doubling of CO2 at anywhere between 0.5°C and 10°C; however, as a consequence of increasingly better data, it appears that the extreme higher and lower values are very unlikely. In fact, as climate science has developed and advanced over time , estimates have converged around 3°C. A summary of recent climate sensitivity studies can be found here.

A study led by Stefan Rahmstorf concluded "many vastly improved models have been developed by a number of climate research centers around the world. Current state-of-the-art climate models span a range of 2.6–4.1°C, most clustering around 3°C" (Rahmstorf 2008). Several studies have put the lower bound of climate sensitivity at about 1.5°C,on the other hand, several others have found that a sensitivity higher than 4.5°C can't be ruled out.

A 2008 study led by James Hansen found that climate sensitivity to "fast feedback processes" is 3°C, but when accounting for longer-term feedbacks (such as ice sheet disintegration, vegetation migration, and greenhouse gas release from soils, tundra or ocean), if atmospheric CO2 remains at the doubled level, the sensitivity increases to 6°C based on paleoclimatic (historical climate) data.

What are the limits on the climate sensitivity value?

Paleoclimate
The main limit on the sensitivity value is that it has to be consistent with paleoclimatic data. A sensitivity which is too low will be inconsistent with past climate changes - basically if there is some large negative feedback which makes the sensitivity too low, it would have prevented the planet from transitioning from ice ages to interglacial periods, for example. Similarly a high climate sensitivity would have caused more and larger past climate changes.

One recent study examining the Palaeocene–Eocene Thermal Maximum (about 55 million years ago), during which the planet warmed 5-9°C, found that "At accepted values for the climate sensitivity to a doubling of the atmospheric CO2 concentration, this rise in CO2 can explain only between 1 and 3.5°C of the warming inferred from proxy records" (Zeebe 2009). This suggests that climate sensitivity may be higher than we currently believe, but it likely isn't lower.

Recent responses to large volcanic eruptions
Climate scientists have also attempted to estimate climate sensitivity based on the response to recent large volcanic eruptions, such as Mount Pinatubo in 1991. Wigley et al. (2005) found:

"Comparisons of observed and modeled coolings after the eruptions of Agung, El Chichón, and Pinatubo give implied climate sensitivities that are consistent with the Intergovernmental Panel on Climate Change (IPCC) range of 1.5–4.5°C. The cooling associated with Pinatubo appears to require a sensitivity above the IPCC lower bound of 1.5°C, and none of the observed eruption responses rules out a sensitivity above 4.5°C."

Similarly, Forster et al. (2006) concluded as follows.

"A climate feedback parameter of 2.3 +/- 1.4 W m-2 K-1 is found. This corresponds to a 1.0–4.1 K range for the equilibrium warming due to a doubling of carbon dioxide"

Recent responses to the 11-year solar cycle

Tung and Camp (2007) noted that

"the annual rate of increase in radiative forcing of the lower atmosphere from solar min to solar max happens to be equivalent to that from a 1% per year increase in greenhouse gases, a rate commonly used in greenhouse-gas emission scenarios [Houghton and et al., 2001]. So it is interesting to compare the magnitude and pattern of the observed solar-cycle response to the transient warming expected due to increasing greenhouse gases in five years."

Tung and Camp were thus able to use satellite-based solar data over 4.5 cycles to calculate an observationally-determined model-independent climate sensitivity of 2.3-4.1°C for a doubling of CO2.
Empirical or 'Instrumental' Observation Methods

Gregory et al. (2002) used observed interior-ocean temperature changes, surface temperature changes measured since 1860, and estimates of anthropogenic and natural radiative forcing of the climate system to estimate its climate sensitivity. They found:

"...we obtain a 90% confidence interval, whose lower bound (the 5th percentile) is 1.6 K. The median is 6.1 K, above the canonical range of 1.5–4.5 K; the mode is 2.1 K."

Recently, several other studies have taken a similar approach and yielded lower equilibrium climate sensitivity estimates, i.e. Ring et al. (2012), Aldrin et al. (2012), Lewis (2013), and Otto et al. (2013), in most cases with central estimates closer to 2°C for a doubling of CO2.

However, Shindell (2014) reconciles the difference between the climate sensitivity estimates in these varying approaches. Shindell notes that the 'empircal' or 'instrumental' approach studies assume that the global mean temperature response to all forcings is equal. His study investigates this assumption by comparing climate model temperature responses to greenhouse gases with their responses to aerosols and ozone.

Shindell, who was a co-author on Otto et al. (2013), notes that “forcing in the NH extratropics [above 30° latitude] causes a greater global mean temperature response than forcing in the tropics”; a result noted by Hansen et al. (1997):

“A forcing at high latitudes yields a larger response than a forcing at low latitudes. This is expected because of the sea ice feedback at high latitudes and the more stable lapse rate at high latitudes”

The forcing from aerosols and ozone isn’t globally uniform, but instead focused more in the northern hemisphere extratropics. Hence it results in a relatively larger temperature response than an equivalent forcing from greenhouse gases, which are well mixed throughout the atmosphere.

When assuming equal sensitivity to all forcings, Shindell estimates the transient climate response (TCR) at 1.0–2.1°C, most likely 1.4°C, which is similar to the estimate in Otto et al. (2013). However, when Shindell accounts for the higher sensitivity to the aerosol and ozone forcings, the estimated TCR range rises to 1.3–3.2°C, most likely 1.7°C. Compared to the IPCC estimated TCR range of 1–2.5°C, and the range in climate models of 1.1–2.6°C, Shindell's results give a low probability for the low end of the range and higher probability for the high end. Given the strong correlation between TCR and equilibrium climate sensitivity, Shindell’s results also suggest that the lower climate sensitivity estimates are unlikely to be accurate.

Examining Past Temperature Projections
In 1988, NASA climate scientist Dr James Hansen produced a groundbreaking study in which he produced a global climate model that calculated future warming based on three different CO2 emissions scenarios labeled A, B, and C (Hansen 1988). Now, after more than 20 years, we are able to review Hansen’s projections.

Hansen's model assumed a rather high climate sensitivity of 4.2°C for a doubling of CO2. His Scenario B has been the closest to reality, with the actual total radiative forcing being about 10% higher than in this emissions scenario. The warming trend predicted in this scenario from 1988 to 2010 was about 0.26°C per decade whereas the measured temperature increase over that period was approximately 0.18°C per decade, or about 40% lower than Scenario B.

Therefore, what Hansen's models and the real-world observations tell us is that climate sensitivity is about 40% below 4.2°C, or once again, right around 3°C for a doubling of atmospheric CO2. For further details, see the Advanced rebuttal to "Hansen's 1988 prediction was wrong."

Probabilistic Estimate Analysis
Annan and Hargreaves (2009) investigated various probabilistic estimates of climate sensitivity, many of which suggested a "worryingly high probability" (greater than 5%) that the sensitivity is in excess of than 6°C for a doubling of CO2. Using a Bayesian statistical approach, this study concluded that

"the long fat tail that is characteristic of all recent estimates of climate sensitivity simply disappears, with an upper 95% probability limit...easily shown to lie close to 4°C, and certainly well below 6°C."

Annan and Hargreaves concluded that the climate sensitivity to a doubling of atmospheric CO2 is probably close to 3°C, it may be higher, but it's probably not much lower.



Figure 3: Probability distribution of climate sensitivity to a doubling of atmospheric CO2 Summary of these results

Knutti and Hegerl (2008) presents a comprehensive, concise overview of our scientific understanding of climate sensitivity. In their paper, they present a figure which neatly encapsulates how various methods of estimating climate sensitivity examining different time periods have yielded consistent results, as the studies described above show. As you can see, the various methodologies are generally consistent with the range of 2-4.5°C, with few methods leaving the possibility of lower values, but several unable to rule out higher values.


Figure 4: Distributions and ranges for climate sensitivity from different lines of evidence. The circle indicates the most likely value. The thin colored bars indicate very likely value (more than 90% probability). The thicker colored bars indicate likely values (more than 66% probability). Dashed lines indicate no robust constraint on an upper bound. The IPCC likely range (2 to 4.5°C) is indicated by the vertical light blue bar.

What Does it all Mean?According to a recent MIT study, we're currently on pace to reach this doubled atmospheric CO2 level by the mid-to-late 21st century.


Figure 5: Projected decadal mean concentrations of CO2. Red solid lines are median, 5%, and 95% for the MIT study, the dashed blue line is the same from the 2003 MIT projection.

So unless we change course, we're looking at a rapid warming over the 21st century. Most climate scientists agree that a 2°C warming is the 'danger limit'. Figure 5 shows temperature rise for a given CO2 level. The dark grey area indicates the climate sensitivity likely range of 2 to 4.5°C.


Figure 6: Relation between atmospheric CO2 concentration and key impacts associated with equilibrium global temperature increase. The most likely warming is indicated for climate sensitivity 3°C (black solid). The likely range (dark grey) is for the climate sensitivity range 2 to 4.5°C. Selected key impacts (some delayed) for several sectors and different temperatures are indicated in the top part of the figure (Knutti and Hegerl 2008)

If we manage to stabilize CO2 levels at 450 ppmv (the atmospheric CO2 concentration as of 2010 is about 390 ppmv), according to the best estimate, we have a probability of less than 50% of meeting the 2°C target. The key impacts associated with 2°C warming can be seen at the top of Figure 6. The tight constraint on the lower limit of climate sensitivity indicates we're looking down the barrel of significant warming in future decades.

As the scientists at RealClimate put it,

"Global warming of 2°C would leave the Earth warmer than it has been in millions of years, a disruption of climate conditions that have been stable for longer than the history of human agriculture. Given the drought that already afflicts Australia, the crumbling of the sea ice in the Arctic, and the increasing storm damage after only 0.8°C of warming so far, calling 2°C a danger limit seems to us pretty cavalier."