(February 14, 2015 at 5:26 am)Aractus Wrote: But really even that is not what climate scepticism is about. Climate scepticism is not about the past and whether nor not CO2 is 50% responsible for the 20th century trend of global warming, but let's assume for argument's sake that it is and that the science is totally 100% settled on that.
If you look at the infrared spectrum which CO2 absorbs you see that the present quantity of CO2 in the atmosphere absorbs nearly the total of what it appears to be capable of absorbing. Let's say that CO2 global mean concentration today is roughly 400ppm, and that we really started this trend back at around 285ppm.
H2O was thought to be responsible for between 90-95% of the greenhouse effect on our planet. That's a large margin for error since it then means the remaining minor gasses are either between 5% to 10% responsible in total. The total greenhouse effect is also not known, it is however estimated.
In recent years those numbers have been revised, it is now believed that H2O is between 36-70% responsible, and CO2 between 9-26%! That's now a much larger margin for error than what was thought ten yeas ago!!
The percent contribution of greenhouse gasses is not a settled science. You pointed this out on how the percent changes as we learn more. So I cannot assume that "science is totally 100% settled on [whether nor not CO2 is 50% responsible]."
Quote:Now to get back to the point. Climate sceptics don't deny that CO2 effects the global temperature - of course it does since it's a GHG. They also don't deny that it contributes to global warming - it should contribute something because it's risen from 285ppm to close to 400ppm.
The things that climate sceptics doubt are these: 1. that greenhouse gasses are the major or primary driver of present climate change; 2. that there's a negative feedback mechanism that makes temperatures "spiral out of control".
Muller's study focusses on the overall deviation from natural. The fact that temperature follows so closely to CO2 rise is surprising. But considering the amount of CO2 increased in the atmosphere, it is not that surprising.
The human produced greenhouse gasses are the major/primary driver of present day climate change. The scientific community agrees.
from IPCC Wrote:Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.[8] This is an advance since the TAR’s conclusion that “most of the observed warming over the last 50 years is likely to have been due to the increase in GHG concentrations.What is not agreed upon is the degree each GHG contributes.
The negative feedback loop depends on the models. Muller's study doesn't address it directly. His study is a comparison of before and after. IPCC is better at handling this question since it takes into account all the intricacies that affect climate.
Quote:There are a further two observations made by the sceptics: 1. that all predictions over the past 20 years have been dramatically wrong and that even the IPCC's predictions for the next 100 years have been progressively scaled down; 2. that while it's true that no one has an alternative explanation for the exact cause of the 20th century warming trend, it's also the case that no one has been able to fully explain prior climate change and what its causes were and in particular the MWP. If we can't explain what caused climate change 1,000 years ago, then what makes us so sure we can explain what is causing climate change today?
Predictions are hard to make when you're working with a choatic system which is what climate is. On the quantitive level, IPCC's predictions are wrong. However, they are not wrong qualitatively. They're model's predictions and data are all pointing to the same conclusion, the earth is warming.
You can go to this link for an in depth talk about MWP. The summary is that whatever caused the MWP is NOT what is causing our warming period.
Quote:Oh the third thing that climate sceptics doubt is that policy can affect the climate. I.e. it's likely that any effort we make to curb CO2 emissions will have a negligible effect on climate change.
I don't understand what how you can doubt that. Anthropogenic GHG are driving warming, so not producing them will slow down warming. When it will slow down and start cooling again is another question entirely.
Quote:Now I should have mentioned this before, but the reason why sceptics have their doubts is because the claims have never been experimentally verified. There have been attempts to experimentally observe the mythical "negative feedback mechanism", and some climate scientists say they have evidence in support of one, whilst others say they have evidence that there isn't one.
Let the climate scientist argue it out amounts themselves about the negative feedback mechanism. The more important point is the world is warming and what we can do about it. The details help answer the logictics of it, but aren't necessary to make the major decisions.
