Comments on: Giving Witness

By: Hayward Maberley

Hayward Maberley — Mon, 13 Jul 2009 00:44:23 +0000

THX1138,
“certain parts of Anchorage are now blighted for home sales as the permafrost has melted so much that houses have subsided & in some cases been swallowed up.”

Well that is in fact another possibe tipping point.
as the vast expanse of permafrost in Siberia and Alaska has started to thaw for the first time since it formed 11,000 years ago. It is caused by the recent 3+°C rise in local temperature over the past 40 years – more than four times the global average. What was until recently a barren expanse of frozen peat is turning into a broken landscape of mud and lakes, some more than a kilometre across. All only in the past 3 or 4 years.

As such upwards of 25% of Planet Earth is underlain to some degree by permafrost and in extreme conditions reaches depths of 1500 meters. This melting has the potential to release vast quantities of methane trapped by ice below the surface – billions of tonnes of methane. World-wide, peat bogs store at least two trillion tons of CO2. This is equivalent to a century of emissions from fossil fuels

By: Hayward Maberley

Hayward Maberley — Sat, 11 Jul 2009 21:59:20 +0000

shockwaver,
From most of the evidence presented, I am inclined to agree that there is AGW.

Low sea levels which existed as far as Australia is concerned from somewhere c.50,000 to 12,500 BP enabled the original inhabitants of the continent to cross:
First the sea gap between Asia/Niugini/Australia as the straits between becam much narrower and shallower;
Then that which now separates Tasmania from mainland Australia. These were are Beringaria
After c12,500 sea levels rose and formed what is now the Bass Strait there and Torres Straight to the North.

These were occasioned by great rises in sea level from the realease of hundreds of thousands of cubic kilometres of ice were stacked up on the continents as glaciers.

As for past tipping points there was a probable one was Meltwater Pulse 1A (mwp-1A), when sea level rose approximately 20 m over a 500 year period about 14,200 years ago. This is a rate of about 40 mm/yr. Recent studies suggest the primary source was meltwater from the Antarctic, perhaps causing the south-to-north cold pulse marked by the Southern Hemisphere Huelmo/Mascardi Cold Reversal, which preceded the Northern Hemisphere Younger Dryas

By: shockwaver

shockwaver — Sat, 11 Jul 2009 14:54:05 +0000

hayward
you seem to have answered the agw question with a gw answer.
most of what you write can be characterized as if-then statements.
what do you think about agw?

By: shockwaver

shockwaver — Fri, 10 Jul 2009 20:09:07 +0000

thx
ocean levels rise and fall. 18,000 years ago the oceans were about 120 meters lower than today. that works out to an average rise of about 7mm/year for 18,000 years. of course sometimes the annual rise was larger than this and sometimes smaller. that is just the average
i believe all of this must have started when the asians came across the exposed bering land bridge (beringia)and the new arrivals started building all those campfires. too much CO2 and not enough soot.

i did check the figures for the last ~century. the average rate of ocean rise has been about 3mm/year. funny thing though, this rate has hardly changed at all since 1880. so to my eye, the data suggest that the heavy industrial CO2 pollution (sic)of the last 50 years has not altered the trend.

just to be on the safe side, i have updated my catastrophe list to add rising oceans:

considering rising oceans, silicone breast implants, swine flu, acid rain, dioxin, red food dyes, cyclamates, ozone depletion, mad cow disease, bee colony collapse, flesh-eating bacteria, pesticide pollution, kudzu strangulation, the millennium bug, killer meteors, cell phone cancer, power line cancer, DDT, china syndrome, saturated fats and the mother of all disasters, global warming, maybe we should all run and hide under the covers.

By: THX1138

THX1138 — Fri, 10 Jul 2009 15:05:00 +0000

Ronnie particulates in the atmosphere from industry, cars, airplane contrails etc reduce the amount of sunlight hitting the surface and therefore tend to cool the planet down I don’t think this is controversial.

I think this was the prog you mentioned I saw it too.

http://www.bbc.co.uk/sn/tvradio/programmes/horizon/dimming_prog_summary.shtml

Clean air legislation could have the unintended consequence of speeding up climate change

By: Ronnie

Ronnie — Fri, 10 Jul 2009 13:11:47 +0000

THX.

I’m a bit dim and I would be grateful if you could explain what you said in greater detail please.

By: THX1138

THX1138 — Fri, 10 Jul 2009 11:46:21 +0000

Ronnie

It’s called global dimming and it’s putting a brake on warming.

By: Ronnie

Ronnie — Fri, 10 Jul 2009 11:42:52 +0000

Rising sea levels are not really about flooding, although that will be bad enough, the real problem is the consequent change in sea temperature and the devastating changes in weather patterns. That has still to come.

I saw a TV programme after 9/11 in which it was shown that during the period when no flights were allowed over the US the temperature actually rose very dramatically. The conclusion being that without carbon emissions acting as a partial mirror reflecting the sun’s heat, things would be much worse.

ladies and gentlemen, I think we are in a no win situation.

By: THX1138

THX1138 — Fri, 10 Jul 2009 10:35:25 +0000

Thanks Hayward for such a detailed post.

I have been reading that actual measurements in the field inc sea level rise, sea ice melt & glacial retreat are in fact worse than the models predict.

Ironically I have read in Field Notes From a Catastrophe, Elizabeth Kolbert from the New Yorkers excellent book that certain parts of Anchorage are now blighted for home sales as the permafrost has melted so much that houses have subsided & in some cases been swallowed up.

The real place to look for climate change is in sea level rise, sea ice and permafrost melt and not in atmospheric temp rise as there is just too much noise.

If you want I can give you the Ice in the drink analogy and how much more energy is required to melt ice but you probably know this all already.

By: Hayward Maberley

Hayward Maberley — Fri, 10 Jul 2009 10:00:43 +0000

THX1138,
AGW is more than happening it is manifesting in many different ways. Tipping points are obvious indicators
Here are 9 scenarios to do with tipping points from
PNAS ISSN 0027-8424 2008 Vol,105 no, 6 pp1786-1793 Timothy M. Lenton et al.
Melting of Arctic sea-ice (approx 10+ years, small uncertainty). As sea-ice melts, it exposes a much darker ocean surface, which absorbs more radiation than white sea-ice so that the warming is amplified. This causes more rapid melting in summer and decreases ice formation in winter. Over the last 16 years ice cover during summer declined markedly. The critical threshold global mean warming may be between 0.5 to 2 degrees Celsius, but could already have been passed. One model shows a nonlinear transition to a potential new stable state with no arctic sea-ice during summer within a few decades.
Decay of the Greenland ice sheet (more than 300 years, small uncertainty). Warming over the ice sheet accelerates ice loss from outlet glaciers and lowers ice altitude at the periphery, which further increases surface temperature and ablation. The exact tipping point for disintegration of the ice sheet is unknown, since current models cannot capture the observed dynamic deglaciation processes accurately. But in a worst case scenario local warming of more than three degrees Celsius could cause the ice sheet to disappear within 300 years. This would result in a rise of sea level of up to seven meters.
Collapse of the West Antarctic ice sheet (more than 300 years, large uncertainty). Recent gravity measurements suggest that the ice sheet is losing mass. Since most of the ice sheet is grounded below sea level the intrusion of ocean water could destabilize it. The tipping point could be reached with a local warming of five to eight degrees Celsius in summer. A worst case scenario shows the ice sheet could collapse within 300 years, possibly raising sea level by as much as five meters.
Collapse of the Atlantic thermohaline circulation (approx 100 years, intermediate uncertainty). The circulation of sea currents in the Atlantic Ocean is driven by seawater that flows to the North Atlantic, cools and sinks at high latitudes. If the inflow of freshwater increases, e.g. from rivers or melting glaciers, or the seawater is warmed, its density would decrease. A global mean warming of three to five degrees Celsius could push the element past the tipping point so that deep water formation stops. Under these conditions the North Atlantic current would be disrupted, sea level in the North Atlantic region would rise and the tropical rain belt would be shifted.
Increase in the El Niño Southern Oscillation (approx 100 years, large uncertainty). The variability of this ocean-atmosphere mode is controlled by the layering of water of different temperatures in the Pacific Ocean and the temperature gradient across the equator. During the globally three degrees Celsius warmer early Pliocene ENSO may have been suppressed in favor of persistent El Niño or La Niña conditions. In response to a warmer stabilized climate, the most realistic models simulate increased El Niño amplitude with no clear change in frequency.
Collapse of the Indian summer monsoon (approx 1+ year, large uncertainty). The monsoon circulation is driven by a land-to-ocean pressure gradient. Greenhouse warming tends to strengthen the monsoon since warmer air can carry more water. Air pollution and land-use that increases the reflection of sunlight tend to weaken it. The Indian summer monsoon could become erratic and in the worst case start to chaotically change between an active and a weak phase within a few years.
Greening of the Sahara/Sahel and disruption of the West African monsoon (approx 10 years, large uncertainty). The amount of rainfall is closely related to vegetation climate feedback and sea surface temperatures of the Atlantic Ocean. Greenhouse gas forcing is expected to increase Sahel rainfall. But a global mean warming of three to five degrees Celsius could cause a collapse of the West African monsoon. This could lead either to drying of the Sahel or to wetting due to increased inflow from the West. A third scenario shows a possible doubling of anomalously dry years by the end of the century.
Dieback of the Amazon rainforest (approx 50 years, large uncertainty). Global warming and deforestation will probably reduce rainfall in the region by up to 30 percent. Lengthening of the dry season, and increases in summer temperatures would make it difficult for the forest to re-establish. Models project dieback of the Amazon rainforest to occur under three to four degrees Celsius global warming within fifty years. Even land-use change alone could potentially bring forest cover to a critical threshold.
Dieback of the Boreal Forest (approx 50 years, large uncertainty). The northern forests exhibit a complex interplay between tree physiology, permafrost and fire. A global mean warming of three to five degrees Celsius could lead to large-scale dieback of the boreal forests within 50 years. Under climate change the trees would be exposed to increasing water stress and peak summer heat and would be more vulnerable to diseases. Temperate tree species will remain excluded due to frost damage in still very cold winters.

That “Collapse of the Atlantic thermohaline circulation”
refers in part to the Gulf Stream. If that were to change to the extent possible, NW Europe would have a climate much like Eastern and Northern Europe, very much colder in winter. With a shorter growing season. And the NE Coast of North America would become colder as well.