Mod Moved Comments To Chat
4 Major rewrite. Word choice and sentences improved.
source | link

The phrase "without some kind of positive feedback mechanism" gives the impression that scientists think there's an alternate mechanism that drives their projected temperatures higher. Climate sensitivity without feedbacks can be calculated fairly accurately on a single sheet of paper, (see here for example) and the result will be approximately 1 deg C. But the result is not relevant to anything, because the real world has many feedbacks; that's why the focus in climate science over the past several decades has been understanding the feedbacks and quantifying their effects. Most of them are well understood, their net effect is overwhelmingly positive (ei.ge. they amplify temperature fluctuations), and of course they are all based on physics, as demonstrated by Chris Colose.

The phrase "without some kind of positive feedback mechanism" gives the impression that scientists think there's an alternate mechanism that drives their projected temperatures higher. Climate sensitivity without feedbacks can be calculated fairly accurately on a single sheet of paper, (see here for example) and the result will be approximately 1 deg C. But the result is not relevant to anything, because the real world has many feedbacks; that's why the focus in climate science over the past several decades has been understanding the feedbacks and quantifying their effects. Most of them are well understood, their net effect is overwhelmingly positive (e.g. they amplify temperature fluctuations), and of course they are all based on physics, as demonstrated by Chris Colose.

The phrase "without some kind of positive feedback mechanism" gives the impression that scientists think there's an alternate mechanism that drives their projected temperatures higher. Climate sensitivity without feedbacks can be calculated fairly accurately on a single sheet of paper, (see here for example) and the result will be approximately 1 deg C. But the result is not relevant to anything, because the real world has many feedbacks; that's why the focus in climate science over the past several decades has been understanding the feedbacks and quantifying their effects. Most of them are well understood, their net effect is overwhelmingly positive (i.e. they amplify temperature fluctuations), and of course they are all based on physics, as demonstrated by Chris Colose.

3 Major rewrite. Word choice and sentences improved.
source | link

The statement is correct, but very misleading. In the absence of the climate system's feedbacks, the climate sensitivity is in fact 1 to 1.2 deg C perfor each doubling of CO2 (per the IPCC). However, the impact of feed backsfeedbacks is actually greater than the direct impact of increased CO2. This can be clearly concludedseen without relying on climate models at all, by looking at the powerful temperature cycles of historical ice ages (or glacial-to-interglacial transitions). These cycles are caused by variations in the Earth's orbit, which only produce a small change in incident radiation. See here for example. Yet Without climate feedbacks, it would take an enormousa much greater change in solar output, or an enormous change in CO2 concentration, to directly cause the observed change in temperaturean ice age. here isChris Colose of Univ. of Wisconsin, Madison provides a good explanation of feedback effects, which states:

To put this in perspective, it would take about five doublings of CO2 or a 7% increase in the total solar radiation hitting the Earth to produce the magnitude of climate change typical of glacial-to-interglacial transitions.

Thus it is clear - without relying on models - that the feedback effect must be greater than the direct effect, or else there could never have been ice ages.

The phrase "without some kind of positive feedback mechanism" gives the impression that scientists have postulated some undefinedthink there's an alternate mechanism in order to drivethat drives their projected temperatures higher. Climate sensitivity without feedbacks can be calculated fairly accurately on a single sheet of paper, (see here for example) and the result will be approximately 1 deg C. But the result is not relevant to anything, because the real world has many feedbacks, sofeedbacks; that's why the focus in climate science over the past several decades has been onunderstanding the feedbacks and quantifying their effects. At this point, most Most of them are well understood, their net effect is overwhelmingly positive (e.g. they amplify temperature fluctuations), and of course they are all solidly based on physics. Reference 2 is a very good explanation, as demonstrated by Chris Colose.

According to James Hansen, the best source of information about feedbacks is not models, but paleoclimate data:s

In the same paper, Hansen calculates the climate sensitivity in various units, and expresses it as 2 to 4 degrees C for a doubling of CO2:

The empirical fast-feedback climate sensitivity that we infer from the LGM-Holocene comparison is thus 5°C/6.5 W/m2 ~ 3⁄4 ± 1⁄4 °C per W/m2 or 3 ± 1°C for doubled CO2. The fact that ice sheet and GHG boundary conditions are actually slow climate feedbacks is irrelevant for the purpose of evaluating the fast-feedback climate sensitivity. 7 This

This empirical climate sensitivity incorporates all fast response feedbacks in the real- world climate system, including changes of water vapor, clouds, aerosols, aerosol effects on clouds, and sea ice. In contrast to climate models, which can only approximate the physical processes and may exclude important processes, the empirical result includes all processes that exist in the real world – and the physics is exact.

As anWater vapor provides a great example of climate feedbacks. Because it absorbs infrared radiation very well, water vapor is a very powerful greenhouse gas. Also, and warmer air holds more water vapor. This is a scientific principal that has been well-understood for over a hundred years. If So, suppose temperature increases because of higher CO2,CO2; the atmosphere will hold more water vapor, which itself will cause a greater greenhouse effectit to absorb more solar radiation, causing it to heat up still further. Calculating the impact of the CO2 while disregarding the water vapor is arbitrarily (or perhaps intentionally) ignoringfeedback would be a significant part of the questionunderestimation for no good reason. Other positive climate feedbacks have similar effectsare also well known to climatologists, such as changes in reflectivity due to melting of snow and ice, release of CO2 from ocean water because of increasing ocean temperatures, and release of methane from melting permafrost.

The statement is correct, but very misleading. In the absence of feedbacks, the climate sensitivity is in fact 1 to 1.2 deg C per the IPCC. However, the impact of feed backs is actually greater than the direct impact of increased CO2. This can be clearly concluded without relying on climate models at all, by looking at historical ice ages. These cycles are caused by variations in the Earth's orbit, which produce a small change in incident radiation. See here for example. Yet it would take an enormous change in solar output or CO2 concentration to directly cause the observed change in temperature. here is a good explanation of feedback effects, which states

To put this in perspective, it would take about five doublings of CO2 or a 7% increase in the total solar radiation hitting the Earth to produce the magnitude of climate change typical of glacial-to-interglacial transitions

Thus it is clear - without relying on models - that the feedback effect must be greater than the direct effect.

The phrase "without some kind of positive feedback mechanism" gives the impression that scientists have postulated some undefined mechanism in order to drive projected temperatures higher. Climate sensitivity without feedbacks can be calculated fairly accurately on a single sheet of paper, (see here for example) and the result will be approximately 1 deg C. But the result is not relevant to anything, because the real world has many feedbacks, so the focus in climate science over the past several decades has been on quantifying their effects. At this point, most of them are well understood, their net effect is overwhelmingly positive, and they are all solidly based on physics. Reference 2 is a very good explanation.

According to James Hansen, the best source of information about feedbacks is not models, but paleoclimate data:

In the same paper, Hansen calculates the climate sensitivity in various units, and expresses it as 2 to 4 degrees C for a doubling of CO2:

The empirical fast-feedback climate sensitivity that we infer from the LGM-Holocene comparison is thus 5°C/6.5 W/m2 ~ 3⁄4 ± 1⁄4 °C per W/m2 or 3 ± 1°C for doubled CO2. The fact that ice sheet and GHG boundary conditions are actually slow climate feedbacks is irrelevant for the purpose of evaluating the fast-feedback climate sensitivity. 7 This empirical climate sensitivity incorporates all fast response feedbacks in the real- world climate system, including changes of water vapor, clouds, aerosols, aerosol effects on clouds, and sea ice. In contrast to climate models, which can only approximate the physical processes and may exclude important processes, the empirical result includes all processes that exist in the real world – and the physics is exact.

As an example of feedbacks, water vapor is a very powerful greenhouse gas, and warmer air holds more water vapor. This is a scientific principal that has been well-understood for over a hundred years. If temperature increases because of higher CO2, the atmosphere will hold more water vapor, which itself will cause a greater greenhouse effect. Calculating the impact of the CO2 while disregarding the water vapor is arbitrarily (or perhaps intentionally) ignoring a significant part of the question. Other feedbacks have similar effects, such as changes in reflectivity due to melting of snow and ice, release of CO2 from ocean water because of increasing ocean temperatures, and release of methane from melting permafrost.

The statement is correct, but very misleading. In the absence of the climate system's feedbacks, the climate sensitivity is 1 to 1.2 deg C for each doubling of CO2 (per the IPCC). However, the impact of feedbacks is greater than the direct impact of increased CO2. This can be seen without relying on climate models by looking at the powerful temperature cycles of historical ice ages (or glacial-to-interglacial transitions). These cycles are caused by variations in the Earth's orbit, which only produce a small change in incident radiation. See here for example. Without climate feedbacks, it would take a much greater change in solar output, or an enormous change in CO2 concentration, to cause an ice age. Chris Colose of Univ. of Wisconsin, Madison provides a good explanation of feedback effects:

To put this in perspective, it would take about five doublings of CO2 or a 7% increase in the total solar radiation hitting the Earth to produce the magnitude of climate change typical of glacial-to-interglacial transitions.

Thus it is clear - without relying on models - that the feedback effect must be greater than the direct effect, or else there could never have been ice ages.

The phrase "without some kind of positive feedback mechanism" gives the impression that scientists think there's an alternate mechanism that drives their projected temperatures higher. Climate sensitivity without feedbacks can be calculated fairly accurately on a single sheet of paper, (see here for example) and the result will be approximately 1 deg C. But the result is not relevant to anything, because the real world has many feedbacks; that's why the focus in climate science over the past several decades has been understanding the feedbacks and quantifying their effects. Most of them are well understood, their net effect is overwhelmingly positive (e.g. they amplify temperature fluctuations), and of course they are all based on physics, as demonstrated by Chris Colose.

According to James Hansen, the best source of information about feedbacks is not models, but paleoclimate data:s

Hansen calculates the climate sensitivity in various units, and expresses it as 2 to 4 degrees C for a doubling of CO2:

The empirical fast-feedback climate sensitivity that we infer from the LGM-Holocene comparison is thus 5°C/6.5 W/m2 ~ 3⁄4 ± 1⁄4 °C per W/m2 or 3 ± 1°C for doubled CO2. The fact that ice sheet and GHG boundary conditions are actually slow climate feedbacks is irrelevant for the purpose of evaluating the fast-feedback climate sensitivity.

This empirical climate sensitivity incorporates all fast response feedbacks in the real- world climate system, including changes of water vapor, clouds, aerosols, aerosol effects on clouds, and sea ice. In contrast to climate models, which can only approximate the physical processes and may exclude important processes, the empirical result includes all processes that exist in the real world – and the physics is exact.

Water vapor provides a great example of climate feedbacks. Because it absorbs infrared radiation very well, water vapor is a very powerful greenhouse gas. Also, warmer air holds more water vapor. So, suppose temperature increases because of higher CO2; the atmosphere will hold more water vapor, which will cause it to absorb more solar radiation, causing it to heat up still further. Calculating the impact of the CO2 while disregarding the water vapor feedback would be a significant underestimation for no good reason. Other positive climate feedbacks are also well known to climatologists, such as changes in reflectivity due to melting of snow and ice, release of CO2 from ocean water because of increasing ocean temperatures, and release of methane from melting permafrost.

2 added 1424 characters in body
source | link

According to James Hansen, the best source of information about feedbacks is not models, but paleoclimate data:

Models are imperfect and we will never be sure that they include all important processes. Fortunately, Earth's history provides a remarkably rich record of how our planet responded to climate forcings in the past. Paleoclimate records yield, by far, our most accurate assessment of climate sensitivity and climate feedbacks.

In the same paper, Hansen calculates the climate sensitivity in various units, and expresses it as 2 to 4 degrees C for a doubling of CO2:

The empirical fast-feedback climate sensitivity that we infer from the LGM-Holocene comparison is thus 5°C/6.5 W/m2 ~ 3⁄4 ± 1⁄4 °C per W/m2 or 3 ± 1°C for doubled CO2. The fact that ice sheet and GHG boundary conditions are actually slow climate feedbacks is irrelevant for the purpose of evaluating the fast-feedback climate sensitivity. 7 This empirical climate sensitivity incorporates all fast response feedbacks in the real- world climate system, including changes of water vapor, clouds, aerosols, aerosol effects on clouds, and sea ice. In contrast to climate models, which can only approximate the physical processes and may exclude important processes, the empirical result includes all processes that exist in the real world – and the physics is exact.

As an example of feedbacks, water vapor is a very powerful greenhouse gas, and warmer air holds more water vapor. This is a scientific principal that has been well-understood for over a hundred years. If temperature increases because of higher CO2, the atmosphere will hold more water vapor, which itself will cause a greater greenhouse effect. Calculating the impact of the CO2 while disregarding the water vapor is arbitrarily (or perhaps intentionally) ignoring a significant part of the question. Other feedbacks have similar effects, such as changes in reflectivity due to melting of snow and ice, release of CO2 from ocean water because of increasing ocean temperatures, and release of methane from melting permafrost.

As an example of feedbacks, water vapor is a very powerful greenhouse gas, and warmer air holds more water vapor. This is a scientific principal that has been well-understood for over a hundred years. If temperature increases because of higher CO2, the atmosphere will hold more water vapor, which itself will cause a greater greenhouse effect. Calculating the impact of the CO2 while disregarding the water vapor is arbitrarily (or perhaps intentionally) ignoring a significant part of the question. Other feedbacks have similar effects, such as changes in reflectivity due to melting of snow and ice, release of CO2 from ocean water because of increasing ocean temperatures, and release of methane from melting permafrost.

According to James Hansen, the best source of information about feedbacks is not models, but paleoclimate data:

Models are imperfect and we will never be sure that they include all important processes. Fortunately, Earth's history provides a remarkably rich record of how our planet responded to climate forcings in the past. Paleoclimate records yield, by far, our most accurate assessment of climate sensitivity and climate feedbacks.

In the same paper, Hansen calculates the climate sensitivity in various units, and expresses it as 2 to 4 degrees C for a doubling of CO2:

The empirical fast-feedback climate sensitivity that we infer from the LGM-Holocene comparison is thus 5°C/6.5 W/m2 ~ 3⁄4 ± 1⁄4 °C per W/m2 or 3 ± 1°C for doubled CO2. The fact that ice sheet and GHG boundary conditions are actually slow climate feedbacks is irrelevant for the purpose of evaluating the fast-feedback climate sensitivity. 7 This empirical climate sensitivity incorporates all fast response feedbacks in the real- world climate system, including changes of water vapor, clouds, aerosols, aerosol effects on clouds, and sea ice. In contrast to climate models, which can only approximate the physical processes and may exclude important processes, the empirical result includes all processes that exist in the real world – and the physics is exact.

As an example of feedbacks, water vapor is a very powerful greenhouse gas, and warmer air holds more water vapor. This is a scientific principal that has been well-understood for over a hundred years. If temperature increases because of higher CO2, the atmosphere will hold more water vapor, which itself will cause a greater greenhouse effect. Calculating the impact of the CO2 while disregarding the water vapor is arbitrarily (or perhaps intentionally) ignoring a significant part of the question. Other feedbacks have similar effects, such as changes in reflectivity due to melting of snow and ice, release of CO2 from ocean water because of increasing ocean temperatures, and release of methane from melting permafrost.

1
source | link