Climate Sensitivity

Tim the plumber wrote:
Climate sensitivity is the amount of additional heat energy going into the energy budget at the surface of the earth. Although there are those who call the final balance temperature produced by this additional energy the sensitivity.

The simple bit is the number of increased Watts per square meter from a doubling of CO2. The general number quoted is about 3.4 W/m2. This is contentious. Lots of debate, lots of differing views. The 3.4 is the IPCC/consensus number.

3.4W/m2 is about +3c final temperature balance.

The complex bit is that the response time for the world is so slow that it will be many many centuries before we get to the balance mostly because of the massive heat capacity of the oceans. Also how do we know what changes the oceans are still dealing with from 500 years ago? All starting to get very very complex.

The next complex thing to hit the fan is that the IPCC claims that there are positive feedback effects which will magnify the inital warming. Lots more debate and no evidecne of such in actual action ever gets presented.

The big problem for the IPCC et al is that they predicted in the early 2000's a rapid warming and no such warming has actually happened. The temperature has been shockingly stable. Possibly a slight warming last year but overall nothing.

Tim the plumber wrote:
Climate sensitivity is the amount of additional heat energy going into the energy budget at the surface of the earth. Although there are those who call the final balance temperature produced by this additional energy the sensitivity.

The simple bit is the number of increased Watts per square meter from a doubling of CO2. The general number quoted is about 3.4 W/m2. This is contentious. Lots of debate, lots of differing views. The 3.4 is the IPCC/consensus number.

3.4W/m2 is about +3c final temperature balance.

The complex bit is that the response time for the world is so slow that it will be many many centuries before we get to the balance mostly because of the massive heat capacity of the oceans. Also how do we know what changes the oceans are still dealing with from 500 years ago? All starting to get very very complex.

The next complex thing to hit the fan is that the IPCC claims that there are positive feedback effects which will magnify the inital warming. Lots more debate and no evidecne of such in actual action ever gets presented.

The big problem for the IPCC et al is that they predicted in the early 2000's a rapid warming and no such warming has actually happened. The temperature has been shockingly stable. Possibly a slight warming last year but overall nothing.

student33 wrote:

Tim the plumber wrote:
Climate sensitivity is the amount of additional heat energy going into the energy budget at the surface of the earth. Although there are those who call the final balance temperature produced by this additional energy the sensitivity.

The simple bit is the number of increased Watts per square meter from a doubling of CO2. The general number quoted is about 3.4 W/m2. This is contentious. Lots of debate, lots of differing views. The 3.4 is the IPCC/consensus number.

3.4W/m2 is about +3c final temperature balance.

The complex bit is that the response time for the world is so slow that it will be many many centuries before we get to the balance mostly because of the massive heat capacity of the oceans. Also how do we know what changes the oceans are still dealing with from 500 years ago? All starting to get very very complex.

The next complex thing to hit the fan is that the IPCC claims that there are positive feedback effects which will magnify the inital warming. Lots more debate and no evidecne of such in actual action ever gets presented.

The big problem for the IPCC et al is that they predicted in the early 2000's a rapid warming and no such warming has actually happened. The temperature has been shockingly stable. Possibly a slight warming last year but overall nothing.

Hi Tim - From what I know and read so far, the fact that the warming projected by the IPCC did not occur was due to (i) a weak Sun (ii) a few major volcanic events (iii) pollution from particulate (PM) matter, especially from an industrialising China - all of which are negative forcings not included in the IPCC's climate sensitivity equation.

student33 wrote:
Hi there - I'm new to climate change and am trying to get my around how it works.

I have a question:

The IPCC in its AR5 use 4 RCPs to project future surface temperatures to the future period 2100. These scenarios are named after values of radiative forcing.

I understand climate sensitivity equation (as given by the IPCC) as:

∆T=∆F x λ x (1-λ c)^(-1)

where ∆F is the radiative forcing.

My question is how do the RCP scenarios 'fit' into climate sensitivity. How do we get from climate sensitivity (which I am assuming to be the fundamental calculation, to the RCP scenarios which project future temperatures - how do the RCPS connect to climate sensitivity - what is the piece of theory / knowledge / that bridges the two things together)?

What is the purpose of climate sensitivity in relation to the IPCC graphs of future temperature projections? How does it fit into projecting these future temperatures? Are calculations of climate sensitivity NEEDED in order to calculate future temperatures, or is it only the radiative forcing ∆F part of the equation that is needed to do so?

Thanks.

Surface Detail wrote:

student33 wrote:
Hi there - I'm new to climate change and am trying to get my around how it works.

I have a question:

The IPCC in its AR5 use 4 RCPs to project future surface temperatures to the future period 2100. These scenarios are named after values of radiative forcing.

I understand climate sensitivity equation (as given by the IPCC) as:

∆T=∆F x λ x (1-λ c)^(-1)

where ∆F is the radiative forcing.

My question is how do the RCP scenarios 'fit' into climate sensitivity. How do we get from climate sensitivity (which I am assuming to be the fundamental calculation, to the RCP scenarios which project future temperatures - how do the RCPS connect to climate sensitivity - what is the piece of theory / knowledge / that bridges the two things together)?

What is the purpose of climate sensitivity in relation to the IPCC graphs of future temperature projections? How does it fit into projecting these future temperatures? Are calculations of climate sensitivity NEEDED in order to calculate future temperatures, or is it only the radiative forcing ∆F part of the equation that is needed to do so?

Thanks.

The RPC (Representative Concentration Pathway) scenarios are simply four possible ways in which greenhouse concentration could develop over the coming years. Each RPC is based on a different assumption of human behaviour over the coming years, ranging from RCP 2.6 (immediate drastic measures to curb GHG emissions) to RCP 8.5 (business as usual). The labels represent the radiative forcing (difference between incoming and outgoing radiation) to be expected for each scenario by the year 2100. The forcings are calculated from the expected levels of GHGs in the atmosphere and other factors under each scenario.

It is only then that climate sensitivity (λ) comes into play. This is the link that gives the final temperature change corresponding to each forcing and is probably where the most uncertainty lies. A low climate sensitivity would mean that a large forcing (from e.g. GHGs, changes in land use) would only cause a small temperature change; a large climate sensitivity would lead to a large temperature change for a relatively small forcing.

Note, though, that climate sensitivity is often expressed not in terms of the forcing required to raise temperature by one degree, but rather in the temperature rise resulting from the equivalent of doubling the CO2 concentration. The IPCC currently estimates this to be about 3°C.