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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Positives and negatives of global warming

What the science says...

Select a level... Basic Intermediate Advanced

Negative impacts of global warming on agriculture, health & environment far outweigh any positives.

Climate Myth...

It's not bad

"By the way, if you’re going to vote for something, vote for warming. Less deaths due to cold, regions more habitable, larger crops, longer growing season. That’s good. Warming helps the poor." (John MacArthur)

At a glance

“It's not going to be too bad”, some people optimistically say. Too right. It's going to be worse than that. There are various forms this argument takes. For example, some like to point out that carbon dioxide (CO2) is plant-food – as if nobody else knew that. It is, but it's just one of a number of essential nutrients such as water and minerals. To be healthy, plants require them all.

We know how climate change disrupts agriculture through more intense droughts, raging floods or soil degradation – we've either experienced these phenomena ourselves or seen them on TV news reports. Where droughts intensify and/or become more prolonged, the very viability of agriculture becomes compromised. You can have all the CO2 in the world but without their water and minerals, the plants will die just the same.

At the same time, increased warming is adversely affecting countries where conditions are already close to the limit beyond which yields reduce or crops entirely fail. Parts of sub-Saharan Africa fall into this category. Elsewhere, many millions of people – about one-sixth of the world’s population - rely on fresh water supplied yearly by mountain glaciers through their natural melt and regrowth cycles. Those water supplies are at risk of failure as the glaciers retreat. Everywhere you look, climate change loads the dice with problems, both now and in the future.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

Most climate change impacts will confer few or no benefits, but may do great harm at considerable costs. We'll look at the picture, sector by sector below figure 1.

IPCC AR6 WGII Chapter 16 Figure FAQ 16.5.1

Figure 1: Simplified presentation of the five Reasons for Concern burning ember diagrams as assessed in IPCC AR6 Working Group 2 Chapter 16 (adapted from Figure 16.15, Figure FAQ 16.5.1).


While CO2 is essential for plant growth, that gas is just one thing they need in order to stay healthy. All agriculture also depends on steady water supplies and climate change is likely to disrupt those in places, both through soil-eroding floods and droughts.

It has been suggested that higher latitudes – Siberia, for example – may become productive due to global warming, but in reality it takes a considerable amount of time (centuries plus) for healthy soils to develop naturally. The soil in Arctic Siberia and nearby territories is generally very poor – peat underlain by permafrost in many places, on top of which sunlight is limited at such high latitudes. Or, as a veg-growing market gardening friend told us, “This whole idea of "we'll be growing grains on the tundra" is just spouted by idiots who haven't grown as much as a carrot in their life and therefore simply don't have a clue that we need intact ecosystems to produce our food.” So there are other reasons why widespread cultivation up there is going to be a tall order.

Agriculture can also be disrupted by wildfires and changes in the timing of the seasons, both of which are already taking place. Changes to grasslands and water supplies can impact grazing and welfare of domestic livestock. Increased warming may also have a greater effect on countries whose climate is already near or at a temperature limit over which yields reduce or crops fail – in parts of the Middle East and sub-Saharan Africa, for example.


Warmer winters would mean fewer deaths, particularly among vulnerable groups like the elderly. However, the very same groups are also highly vulnerable to heatwaves. On a warmer planet, excess deaths caused by heatwaves are expected to be approximately five times higher than winter deaths prevented.

In addition, it is widely understood that as warmer conditions spread polewards, that will also encourage the migration of disease-bearing insects like mosquitoes, ticks and so on. So long as they have habitat and agreeable temperatures to suit their requirements, they'll make themselves at home. Just as one example out of many, malaria is already appearing in places it hasn’t been seen before.

Polar Melting

While the opening of a year-round ice-free Arctic passage between the Atlantic and Pacific oceans would have some commercial benefits, these are considerably outweighed by the negatives. Detrimental effects include increased iceberg hazards to shipping and loss of ice albedo (the reflection of sunshine) due to melting sea-ice allowing the ocean to absorb more incoming solar radiation. The latter is a good example of a positive climate feedback. Ice melts away, waters absorb more energy and warming waters increase glacier melt around the coastlines of adjacent lands.

Warmer ocean water also raises the temperature of submerged Arctic permafrost, which then releases methane, a very potent greenhouse gas. The latter process has been observed occurring in the waters of the East Siberian Arctic Shelf and is poorly understood. At the other end of the planet, melting and break-up of the Antarctic ice shelves will speed up the land-glaciers they hold back, thereby adding significantly to sea-level rise.

Ocean Acidification

Acidity is measured by the pH scale (0 = highly acidic, 7 = neutral, 14 = highly alkaline). The lowering of ocean pH is a cause for considerable concern without any counter-benefits at all. This process is caused by additional CO2 being absorbed in the water. Why that's a problem is because critters that build their shells out of calcium carbonate, such as bivalves, snails and many others, may find that carbonate dissolving faster than they can make it. The impact that would have on the marine food-chain should be self-evident.

Melting Glaciers

The effects of glaciers melting are largely detrimental and some have already been mentioned. But a major impact would be that many millions of people (one-sixth of the world’s population) depend on fresh water supplied each year by the seasonal melt and regrowth cycles of glaciers. Melt them and those water supplies, vital not just for drinking but for agriculture, will fail.

Sea Level Rise

Many parts of the world are low-lying and will be severely affected even by modest sea level rises. Rice paddies are already becoming inundated with salt water, destroying the crops. Seawater is contaminating rivers as it mixes with fresh water further upstream, and aquifers are becoming saline. The viability of some coastal communities is already under discussion, since raised sea levels in combination with seasonal storms will lead to worse flooding as waves overtop more sea defences.


Positive effects of climate change may include greener rainforests and enhanced plant growth in the Amazon, increased vegetation in northern latitudes and possible increases in plankton biomass in some parts of the ocean.

Negative responses may include some or all of the following: further expansion of oxygen-poor ocean “dead zones”, contamination or exhaustion of fresh water supplies, increased incidence of natural fires and extensive vegetation die-off due to droughts. Increased risk of coral extinction, changes in migration patterns of birds and animals, changes in seasonal timing and disruption to food chains: all of these processes point towards widespread species loss.


Economic impacts of climate change are highly likely to be catastrophic, while there have been very few benefits projected at all. As long ago as 2006, the Stern Report made clear the overall pattern of economic distress and that prevention was far cheaper than adaptation.

Scenarios projected in IPCC reports have repeatedly warned of massive future migrations due to unprecedented disruptions to global agriculture, trade, transport, energy supplies, labour markets, banking and finance, investment and insurance. Such disturbances would wreak havoc on the stability of both developed and developing nations and they substantially increase the risk of future conflicts. Furthermore, it is widely accepted that the detrimental effects of climate change will be visited mostly on those countries least equipped to cope with it, socially or economically.

These and other areas of concern are covered in far more detail in the 36-page Summary for Policymakers from the IPCC AR6 Synthesis Report, released in March 2023. The report spells out in no uncertain terms the increasingly serious issues Mankind faces; the longer that meaningful action on climate is neglected, the greater the severity of impacts. The report is available for download here.


Last updated on 21 April 2023 by John Mason. View Archives

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Further reading

National Geographic have an informative article listing the various positives and negatives of global warming for Greenland.

Climate Wizard is an interactive tool that lets you examine projected temperature and precipitation changes for any part of the world.

A good overview of the impacts of ocean acidification is found in Ken Caldeira's What Corals are Dying to Tell Us About CO2 and Ocean Acidification

Denial101x video

Here is a related video lecture from Denial101x - Making senses of climate science denial


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Comments 201 to 225 out of 405:

  1. You write: Agriculture: "the amount of sunlight reaching the ground in summer will not change because it is governed by the tilt of the earth." All of Northern Europe, lush with agriculture and forests, is at the same latitude as the Canadian tundra where the brutal cold kills all trees, with only lichens surviving. Your argument is simply wrong.
  2. Er ... Manny, can you explain your reasoning a little more? At a given latitude, on a revolving Earth, during a given 24-hour period, the amount of sunlight arriving will be the same at all longitudes, excluding the chances of a massive and short-lived sunspot occurring during that 24 hours. How do you work out that insolation will differ? The temperature difference you mention results form causes other than insolation, I would have thought.
  3. Manny, Charles C. Mann has a quite readable chapter devoted to the spread of malaria post-1492 in his recent book 1493. The story is a little more complicated than you indicate. There is a range of malaria-carrying mosquitoes. There is also a range of human responses, based on genetics. The Canadian malaria mentioned was probably vivax rather than the falciparum mentioned in Epstein.
  4. And, Manny, I agree with Doug. What you're trying to say with the comparison between Canada and Europe is as clear as mud.
  5. Mohyla103:
    Bernard J.: "Glaciers do not impound water, they hold it as frozen mass." Did you mean that glaciers can be actual dams that hold liquid water back behind them, or that glaciers act like a dam in that they hold precipitation (snow, not rain) at a higher altitude? If it is the latter, then I misunderstood the phrase "natural dam" in your original statement.
    Although I know what his answer is, you'd best direct the question at Tom Curtis, as he was the one who originally used the phrase. For someone who said:
    It's this attitude of alarming the public with misleading claims that make me skeptical of AGW reporting accuracy in general.
    it's important to ensure that you are not transferring your own misunderstandings on to those who are in fact reporting accurately. This would seem to apply more broadly to your commentary here, as much of your scepticism appears to originate from a confusion over the actual science, and/or about what people mean when they report it.
  6. I think Manny is confused as to why you have latitudal variation in climate. It is not due to differences insolation but to the many local influences on climate. For northern Europe, the warm Gulf Steam is the major factor.
  7. Bernard J @205, Mohyla has mistaken a simile for a literal description. As the "mistake" involves a typically ridiculous interpretation, there was IMO no basis for it. Therefore I presumed the "mistake" to be a debating technique and discussion with Mohyla to necessarily to be fruitless in that once people start to intentionally misunderstand you, they are not interested in sincere discussion.
  8. DSL @203, interesting about Plasmodium vivax. That it was not Plasmodium falciparum is made clear by the death rate of just 3% of those hospitalized with an infection in 1823. In contrast, Plasmodium falciparum that it creates a selective advantage for the sickle cell anemia gene which, though fatal if received from both parents, grants resistance to malaria if received from just one. The result is the strong correlation between Plasmodium falciparum and frequency of the gene for sickle cell anemia in the population (see maps below). Of course, the concern with global warming is not the spread of vivax but of falciparum.
  9. Doug H @202, I believe Manny has raised a legitimate point. The issue is that more than one factor can limit the growth of plants. With regard to energy, plants have two important sources of energy. Like all "cold blooded" creatures, the energy which drives the brownian motion within their cells, and hence powers the chemical operations of life comes from the environment, and is a simple consequence of the local surface temperature. As the temperature rises, the brownian motion becomes more vigorous so that chemical reactions (and hence growth) proceeds faster. Of coure, the characteristic of energy from the environment as heat is that it has a high entropy. Life cannot proceed without some reactions that result in a lower entropy than their surrounds, so all life also requires access to a low entropy energy source to drive these reactions. For plants, that is the energy from sunlight which they convert to low entropy sugars or starches. This does mean that at higher latitudes, available sunlight becomes a restriction of plant growth no matter what the temperature, because without sunlight there is no low entropy energy to drive the low entropy reactions that life needs. What Manny has pointed out is that, given that there is extensive forestation in western Europe at the same latitudes as the Canadian sub-arctic, it is the high entropy energy from the environment (warmth) which is the primary limiting factor at those latitudes. The assumption it was lack of the low entropy sunlight that restricted growth was not warranted. Indeed, given that plants do not just lie flat to the surface, but deploy their leaves to gain maximum sunlight, it is not clear that the geometric argument about sunlight carries any weight. Given that in a past era, there were forest at the South Pole, I would suggest that lack of direct sunlight is only ever a seasonal limitation of the growth of plants.
  10. Tom Curtis @ 209, thanks for the extra info - I am always confronted with just how little I know about anything! I must admit, I had never given a thought to the low entropy/high entropy energy source argument, so I have learned something new today - thank you. On the other hand, I was responding to Manny's dismissal of this:
    "the amount of sunlight reaching the ground in summer will not change because it is governed by the tilt of the earth."
    by saying this
    Your argument is simply wrong.
    which seemed like a drive-by pot-shot.
  11. Doug H @210, it struck me the same way. That does not, however, it did not hit the target.
  12. 211, Tom, While Manny's (and your) argument concerning sunlight versus temperature (i.e. multiple limiting factors on growth) is applicable to the case of plant life in general, we are talking specifically about crops that are useful for agriculture, and that produce a reasonable yield. Both yield and crop type are dependent on length of growing season among other factors. If you reference this map you can see that productivity for all northern latitudes is severely hampered (note that the coloration for Alaska is certainly wrong... it's been colored as a part of the USA, I'm sure, and not relative to its own actual crop yields). In particular, you will note that corn is never grown at northern latitudes. It must generally be planted in May and is not ready to harvest until October. When you add the problems with soil (much of the soil in northern latitudes having been scraped clean by glacial action, with no chance for later plant growth to replenish the soil), chances of achieving "good" crop productivity in northern latitudes due to climate change do not look promising. In my own direct experience, some years back I had a tremendous tomato garden on the south side of the house, despite being too far north to really expect to get good tomatoes. Being right against the foundation and chimney, the ground got very warm, and it was the one part of my property (ringed by trees) that got good sunlight through the growing season. The only drawback was that as the sun moved further south in August (just as the fruit should be reaching maturity), it would begin to dip below the tree line and shorten the length of the day. After about five years, my tomatoes wouldn't ripen. The trees at the south side of my property had continued to grow taller and to encroach over my lawn, with the end result that they cut off the sunlight too soon. I had lush, wonderful plants covered with fruit that never came close to maturity.
    Response: [JH] Fried green tomatoes? (:
  13. Bernard J. @ 205 You're right, of course, that question should have been directed at Tom Curtis. I didn't notice a third person had entered the glaciers as natural dams discussion. Sorry to you and Tom Curtis for the mixup. I am all for clearing up misunderstandings, which is precisely why I asked the question. It wasn't until I read your post saying glaciers "do not impound water" that I realized there must be some misunderstanding because that is exactly what a literal dam does. My misunderstanding was not intentional. "...much of your scepticism appears to originate from a confusion over the actual science, and/or about what people mean when they report it." I'm not sure what other cases you're referring to? I will refer you to post 199 and the discussion with JMurphy leading up to it, where I showed that in fact my reading of the original sources was correct and it was Barnett who was confused and/or did not report data accurately in his paper. Clearing up misunderstandings is a good thing, be they my own or ones in published papers.
  14. Tom Curtis @ 207 "Mohyla has mistaken a simile for a literal description. As the "mistake" involves a typically ridiculous interpretation, there was IMO no basis for it." You said that glaciers act as "natural dams", so I thought you meant: natural - it's a glacier, not man-made, therefore it's natural dam - something that holds back liquid water in a river system Please explain how my interpretation was "typically ridiculous"? It seems like quite a reasonable, if incorrect, interpretation to me. "Therefore I presumed the "mistake" to be a debating technique and discussion with Mohyla to necessarily to be fruitless in that once people start to intentionally misunderstand you, they are not interested in sincere discussion." I most certainly did not "intentionally" misunderstand you and to suggest I did is rude and debasing. Thank a lot for simply ignoring my mistake and assuming I was just out to cause trouble for the sake of trouble, instead of trying to further clarify your meaning first. It seems you have overestimated my intelligence here. I will ask once more, this time to the correct person. Please understand this is a sincere question: Did you mean: 1) that glaciers act as true barriers that hold liquid water back behind them, and prevent/control its release downstream? or 2) that glaciers act somewhat like a dam in that they hold precipitation (in the form of snow and ice) at a higher altitude? or 3) something else?
  15. Mohyla @214, how can it be a sincere question when the question has already been answered?
  16. Sphaerica @212, I think the map is suspect in sustaining your point. The distribution of rice, wheat and corn production are clearly heavily influenced by demand side economic factors. Further, they clearly take a nation wide average so that Australia's vast deserts result in low or medium productivity despite Australia having some of the richest and most extensive wheat growing regions in the world. Transferring this to Canada, it means the current limited arability of the Canadian Arctic is averaged with the southern wheat growing areas of Canada, and are not indicative of grain productivity in those southern areas. Having said that, your more general point is well taken. With a six month growing season, it is difficult to imagine corn prospering within the Arctic circle, not matter what the temperature. Never-the-less, a there is substantial room for a northward shift in Canadian agricultural production before the Arctic Circle is reached. The projected 2050 wheat production areas below are well south of the Arctic Circle: On the other hand, a similar northward migration of wheat production between 2050 and 2100 would bring the northern regions of production within the Arctic Circle and a possible hard limit on northerly extent on production. As you say, the situation is complicated, but clearly the notion that a northerly migration of agriculture under business as usual will compensate for loss of productivity in tropical and temperate lands is not sustainable (either intellectual, or into the future). The situation is worse in the Southern Hemisphere with a definite hard limit on production in the form of the southern coast lines of the continents.
  17. Tom Curtis @215 It seems I can't convince you of my sincerity, but I hope you will give me the benefit of the doubt anyway and continue the discussion. A simple direct answer from you would be more helpful in avoiding misunderstanding. Nevertheless, I think I understand now that you originally meant (2), but I interpreted it as (1), as (2) is a simile and (1) is the literal description. (?) You had originally said in 178 that these natural dams can absorb large precipitation events. I thought this meant it helped the watershed absorb the precipitation (rain) by holding the water behind it, like a dam. I wasn't sure I understood this correctly at the time so I searched online about glaciers as natural dams and all I found were articles about glacial ice or moraine dams, glacial lakes and outburst floods. I invite you to try this search yourself, and hopefully you will understand that me interpreting "natural dams" literally was not "typically ridiculous" but a natural misunderstanding of the phrase. Since your intended meaning seems to be like (2) could this have been better phrased as "glaciers act as natural reservoirs" since you seem to be referring to precipitation held in the glacier itself, not blocked up behind it in a glacial lake? Or am I still way off?
  18. Tom Curtis @217 Correction: could this have been better phrased as "glaciers act as natural frozen reservoirs"?
  19. mohyla103 - That's clearly what Tom Curtis meant, it certainly was my interpretation when I read his original post, and at this point I should think the issue is clarified. Both snowpacks and glaciers (as, essentially, snowpack compressed to ice, undergoing flow through internal deformation under their own weight) are reservoirs of winter precipitation, feeding freshwater supplies down hill. Perhaps we could move on, now???
  20. KR Thank you for the direct answer. Sorry to all for cluttering the board with this but it truly was a misunderstanding. Yes, moving on then I do have one final question. Tom Curtis said that glaciers can absorb large precipitation events and thus help prevent floods. How does this happen? If it's snow, I understand a glacier can absorb it. However, wouldn't this snow still be available for later use downstream upon melting, regardless of whether it lands on a glacier or the ground? How does snow's absorption by a glacier confer an advantage or help prevent flooding? If it's rain, I don't understand how a glacier absorbs it at all. Logicman in post 176 said that rainwater just runs off glaciers and does not add to its mass. This seems reasonable and nobody corrected this but was he oversimplifying?
  21. mohyla103 - Please note that large precipitation events on glaciers will generally be snow - being on the tops of mountains, and all that. Rate of flow from a glacier is dependent upon melt at the base end of the glacier, not recent precipitation at the top (which affects available glacial melt mass years to multiple decades later). Snowpack, on the other hand, melts yearly. You won't see a lot of rain on glacial origin locations...
  22. I still don't understand how a glacier can absorb a large precipitation event (of snow) and help prevent flooding. A large dump of snow would not come rushing down the mountain all at once anyway, since it's not liquid. Presumably this large dump would melt slowly throughout the spring, and possibly into the summer. This seems like pretty good flood control. Obviously I'm missing something here... what is it? "Please note that large precipitation events on glaciers will generally be snow - being on the tops of mountains, and all that." Certainly rain is possible on some glaciers during summer days. The temperature can be warmer and even above freezing, it being summer, and all that. I'll take your sentence to mean that discussion of rain events is not relevant here, though.
  23. @ mohyla103 Precipitation falling on a glacier is a case-dependent thing. Remember that the mass-balance of a glacier is a dynamic output of gains in the accumulation zone factored against losses in the ablation zone. Other variables are temperature, insolation, form of the precipitation, etc. That precipitation falling in the accumulation as snow typically gets compacted over time and eventually is converted into ice. During the summer melt, even the accumulation zone may contain melt pools or even melt lakes. These are drained via moulins into the body of the ice mass into the internal plumbing drainwork of the glacier. That precipitation falling as rain will largely be carried off via runoff of the outside of the glacier or into the interior plumbing. Glaciers not at their terminal extent often have a lake that forms at the terminal end of the glacier, impounded between the icy tongue of the glacier and the terminal moraine of rock, silt and soil that serves the function of a dam. These glacial dam-formed lakes can empty and fill according to the mass-balance of the glacier. High melt seasons can fill the lake beyond capacity, sometimes resulting into a catastrophic collapse and flood. When these occur, many thousands of people living in the flood plains below can perish in the massive walls of water and mud that ensue. How warming is affecting alpine glaciers is the reduction of the accumulation zones and the increases of the ablation zones. The result is a tilting of the vast majority of the mass-balances of the alpine glaciers of the world. Even those of the Himalayas (a post on this is in the works). HTH. Some resources for you:
  24. Daniel Bailey, thanks for your detailed explanation and links. I learned, among other things, that snow cover in the accumulation zone throughout the summer and not just snowfall in the winter is necessary to maintain the glacier's mass balance. The thing I don't understand is from post 178 from Tom Curtis. Since I'm not sure if he will answer me or not, perhaps you could help clarify this? He said that glaciers "help prevent floods, and prevent seasonal water shortages". I understand how they prevent seasonal water shortages, but how do they help prevent floods?
  25. mohyla I admire your persistence. Glaciers that do receive large rain events are generally in temperate settings. Take southern Alaska. During such rain storms not only do we have the precipitation from rain, but this also causes quite a bit of snow melt. Thus, the actual water that will drain off per unit area can be greater than elsewhere. However, glacier plumbing systems filtering the water through the snowpack etc is slow. This spreads out the increased discharge and does not lead to a spike that triggers floods. If we take the Himalaya summer monsoon than rain only falls low on the glacier and again the drainage system is not as efficient as non-glaciated areas.

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