Some observed and potential effects of global warming are positive feedbacks, which contribute directly to further global warming. The Intergovernmental Panel on Climate Change's (IPCC) Fourth Assessment Report states that "Anthropogenic warming could lead to some effects that are abrupt or irreversible, depending upon the rate and magnitude of the climate change."[6]

Carbon cycle feedbacks

There have been predictions, and some evidence, that global warming might cause loss of carbon from terrestrial ecosystems, leading to an increase of atmospheric CO2 levels. Several climate models indicate that global warming through the 21st century could be accelerated by the response of the terrestrial carbon cycle to such warming.[7] All 11 models in the C4MIP study found that a larger fraction of anthropogenic CO2 will stay airborne if climate change is accounted for. By the end of the twenty-first century, this additional CO2 varied between 20 and 200 ppm for the two extreme models, the majority of the models lying between 50 and 100 ppm. The higher CO2 levels led to an additional climate warming ranging between 0.1° and 1.5 °C. However, there was still a large uncertainty on the magnitude of these sensitivities. Eight models attributed most of the changes to the land, while three attributed it to the ocean.[8] The strongest feedbacks in these cases are due to increased respiration of carbon from soils throughout the high latitude boreal forests of the Northern Hemisphere. One model in particular (HadCM3) indicates a secondary carbon cycle feedback due to the loss of much of the Amazon Rainforest in response to significantly reduced precipitation over tropical South America.[9] While models disagree on the strength of any terrestrial carbon cycle feedback, they each suggest any such feedback would accelerate global warming.

Observations show that soils in the U.K have been losing carbon at the rate of four million tonnes a year for the past 25 years[10] according to a paper in Nature by Bellamy et al. in September 2005, who note that these results are unlikely to be explained by land use changes. Results such as this rely on a dense sampling network and thus are not available on a global scale. Extrapolating to all of the United Kingdom, they estimate annual losses of 13 million tons per year. This is as much as the annual reductions in carbon dioxide emissions achieved by the UK under the Kyoto Treaty (12.7 million tons of carbon per year).[11]

It has also been suggested (by Chris Freeman) that the release of dissolved organic carbon (DOC) from peat bogs into water courses (from which it would in turn enter the atmosphere) constitutes a positive feedback for global warming. The carbon currently stored in peatlands (390–455 gigatonnes, one-third of the total land-based carbon store) is over half the amount of carbon already in the atmosphere.[12] DOC levels in water courses are observably rising; Freeman's hypothesis is that, not elevated temperatures, but elevated levels of atmospheric CO2 are responsible, through stimulation of primary productivity.[13][14]

Tree deaths are believed to be increasing as a result of climate change, which is a positive feedback effect.[15]

Arctic methane release

Warming is also the triggering variable for the release of carbon (potentially as methane) in the arctic.[16] Methane released from thawing permafrost such as the frozen peat bogs in Siberia, and from methane clathrate on the sea floor, creates a positive feedback.[17][18]

Methane release from melting permafrost peat bogs

Wikinews has related news: Scientists warn thawing Siberia may trigger global meltdown
Western Siberia is the world's largest peat bog, a one million square kilometer region of permafrost peat bog that was formed 11,000 years ago at the end of the last ice age. The melting of its permafrost is likely to lead to the release, over decades, of large quantities of methane. As much as 70,000 million tonnes of methane, an extremely effective greenhouse gas, might be released over the next few decades, creating an additional source of greenhouse gas emissions.[19] Similar melting has been observed in eastern Siberia.[20] Lawrence et al. (2008) suggest that a rapid melting of Arctic sea ice may start a feedback loop that rapidly melts Arctic permafrost, triggering further warming. ...

Plimer talks nonsense and I doubt he wrote the book that bears his name. I read and post scientific papers.

Jovial Monk wrote on Aug 8^th, 2018 at 3:57pm:

If the globe was actually warming up there would be higher temps everywhere no record cold temps etc...

Maybe MBP you'd like to try again.  Or wait another 30 years and maybe just maybe your alarmism might be more realistic.