jeremyduncombe":1s4e55jx said:
Cheshirechappie":1s4e55jx said:
jeremyduncombe":1s4e55jx said:
That is partly true. Increased CO2 concentrations will give an initial boost to plant growth, and so do increasing temperatures. However, when average temperatures pass a certain point, a plant’s ability to absorb and use carbon dioxide reduces. If we all accept that increasing atmospheric CO2 ( whether manmade or not ) eventually leads to global warming, we will sooner or later reach a point when plant growth slows sharply and CO2 levels therefore increase ever faster. I don’t know when or whether we will get to that point - but maybe it would be better not to find out the hard way.
That's interesting. Would you be kind enough to provide a link or two, or indicate at what temperature a plant's ability to absorb carbon dioxide reduces, and by how much it's ability to absorb reduces? Does this happen at one or two degrees centigrade above current temperatures (which seems rather improbable, given that most plants grow better in summer conditions than winter ones), or at tens of degrees centigrade above (which even the most alarmist forecasts of global warming fall short of)?
If you want some rather heavy bedtime reading, try this:
https://nph.onlinelibrary.wiley.com/doi ... /nph.15283.
It can be summarised ( very roughly! ) as:
1) A bit of warming probably increases CO2 uptake by many plants;
2) A lot of warming probably reduces CO2 absorption by many plants. Some trees may be able to acclimatise to higher temperatures, but others may not;
3) But ( from this and lots of other studies ) the biggest effect seems to be from increased global temperatures increasing drought risks across large areas of the globe, with consequent reductions in plant growth.
So I can’t quote a temperature rise at which effects will suddenly happen. Some areas are already experiencing more frequent droughts and lower growth, but it is always difficult to pin this directly on climate change. The only thing I can safely say is that rising atmospheric CO2 will not automatically lead to faster plant growth, and may eventually lead to the opposite.
No sign of a drought in my garden right now.
Thanks for the reply. Given the nature of these 'debates' in the past, I wasn't really expecting one!
Here's a passage from page 425 of 'Heaven and Earth' by Ian Plimer:
"During times of ice ages such as 140,000 years ago, the carbon dioxide content of the atmosphere was higher than the pre-industrial revolution figure of 270ppmv [reference to Lorius et al 1990: The ice core record - climate sensitivity and future greenhouse warming, Nature 347 pp 139-145]. It is clear that CO2 is not the only factor that controls air temperature, otherwise we could not have ice age conditions with a high atmospheric CO2 content. The transition to global ice age to global warming at about 250Ma was characterised by huge rises (to 2000ppmv) and falls (to 280ppmv) in the amount of atmospheric CO2 [Montanez et al 2007 - CO2 forced climate and vegetation instability during the Late Paleozoic deglaciation. Science 315 pp87-91]. During this time plant and animal life thrived. If CO2 was not recycled and humans burned all the known fossil fuels on earth, then the atmospheric CO2 content would be 2000ppmv."
I think that both your reference and mine were written by people of knowledge, decency and integrity, but their messages do seem to vary a bit, or our interpretations do, at any rate.
Which just demonstrates how complex and uncertain 'climate science' (as opposed to climate politics) tends to be. It's deeply regrettable that most of our media fail lamentably to look at any depth at climate science, but I suppose that trying to convey complexity is a lot harder than simple dumbed-down soundbites. Either the journalists think we couldn't cope with the complexity, or, more likely, some of journalists can't. It's also deeply regrettable that the science and the politics have become so entangled that separating the two is a nightmare.
I've seen very credible evidence that climate change is predominantly a natural phenomenon, but there are plenty asserting that it's current changes are predominantly anthropogenic.
Where does the truth of all this lie? Damned if I know - but I strongly suspect that the political ramifications are going to cause me inconvenience, curb my freedom to act as I see fit, and cost me a lot of money. Matthew Goodwin, author (with Roger Eatwell) of 'National Populism; The Revolt against Liberal Democracy' has suggested that the next big political argument, after the debates surrounding EU membership, will be about 'environmentalism' and it's ramifications, and I suspect he may be right.
We shall no doubt find out in due course.