I'm gonna have to chuck my 4 happen'eth in here.
I do not think anybody believes that the AGW driver in any way challenges 'natural' drivers atm? (except in the Arctic?) but it is a driver that is a constant pressure and that pressure grows over time. Natural drivers wax and wane and so either augment or detract from the AGW driver over their phase. They either combine (and cancel) or combine (and augment) or appear as singles but all along you now need to add in the AGW forcing.
Some folk pooh pooh the notion of 'tipping points' but I find them very difficult to dismiss. Take the Arctic for e.g. If we have warm phase on warm phase plus the AGW Driver we could find a massive collapse event occurring in Greenland say (or massive methane release off Siberia). Even when the naturals subside the impacts of that warm forcing (above and beyond what pure natural could muster) remains and feeds back into the system (be it sea level hike/ocean current impacts or ,for the methane, temp hikes due to GHG forcing) making it ever easier to find disruption outside of pure 'natural further down the line.
The last 'El -Nino' was nothing special but due to the global temp hikes since the 'super' Nino of 98' this moderate Nino pushed temps to near those achieved by the super of 98'. The next El-Nino will surely punch through this record global temp without much hassle? And if we were to have another 'Super Nino'?
The slow 'drip drip' melting of the Arctic ice mass allowed for the mass loss we saw in 07' (25% higher than ever recorded) Did we recover any mass since that time? What will happen when we see the next 'perfect storm' synoptic (3 to 13yrs away)? if we think ice loss is now messing in global circulation then what will such an event will lead to in global circulation?
The changes in the Arctic have been a mixture of natural and AGW but the slow 'drip,drip' of AGW wins out due to it's constant presence even amid negative natural phases. The same with Global temps. Cold phases used to show but I would very much suspect that the past 13 years should have been a cooling phase (akin to the 60's/early 70's?) but the presence of the upward trend has effectively offset this 'cooling' leaving what we have seen. Should I be proven correct then what will the next 'warm phase' be like? normal or warmer than we have ever seen before (in our recorded history)?
We are now at a point to test the 'tipping point' theory for real. I feel we have already seen the first in the Arctic sea ice with ice mass tripping over the 'tipping point' in the mid 80's. One of the next ones we may see will be Methane loss over the Arctic. This will occur either during our next global 'warm phase' with permafrost melt ponds putting significant increases in methane output into the atmosphere as to lead to a sudden global warming leading to continued releases and further warming negating 'natural negative temp forcings' leaving only warming, the other would be massive sudden releases of hydrate from the offshore submerged permafrosts off Siberia. We must be mindful that Arctic methane releases now equals the combined outputs from all the worlds oceans.
To recap, AGW is small but constant and growing. eventually it will outweigh any 'natural cold drivers' and this will be hastened by it combining with 'natural warm drivers'.
No body thinks that AGW equates to CO2 alone. If you look at land use changes across the tropical zone you can see the scale of 'man made' changes occurring there. in my school days (1970's) we were campaigning to 'save the Rainforest's' but the destruction there continues apace. If you look at the local impact on weather/climate across a Forrest and a pampas it does not take much to expand this into a regional then global impact on weather/climate.
When we look at the sub Saharan increase in desert due to mans unsustainable agriculture there over the same period we see another 'local' climate change. How many 'local' climate changes equates to a global change?
Nature used to have a kind of ad hoc balance. Now it has had this balance impacted by changes that are far faster and extensive than She can soak up and cope with. The Carbon reserves that we have releases are on top and above of the 'natural carbon cycle ' as was must throw this system off balance? If we believe the geological record then such releases by similar deposits being subducted at plate margins ( and the carbon released in volcanic activity) have lead to global climate change of a scale similar to those predicted by most of the leading authorities studying AGW.
Originally Posted by: Gray-Wolf