It's enough to make a lot of marginally-livable places completely unlivable. It's enough to throw off growing seasons, costing a significant amount of agriculture. It will require more water, already a tough squeeze in a lot of places. It will melt a lot of ice, causing disruptions to sea level that will make expensive storms more frequent. It will throw off rain patterns, meaning that some places will become arable that weren't, but forcing some existing farms to stop. That will be hugely disruptive and expensive.
The real problem is that it likely won't just be 3.2F. That's actually pretty much what the IPCC's target is: they want it to be just 3.2F (2C). But even that much involves drastically cutting CO2 output: CO2 is very stable and will last for many centuries. We will continue to get warmer for decades even if we stopped burning fossil fuels utterly, right this instant.
Instead, the world as a whole has continued to increase its CO2. (The US has actually gone back down to 1990 levels, largely because of a shift from coal to natural gas, but partly due to renewables.) That means we're on a track for more like 6F to 8F by 2100, and that is pretty clearly a lot.
One analogy I use is: imagine sitting in a pool with friends, and one person starts pushing one of those floating lounge chairs up and down. They might only increase the average height of the water by a millimeter or so, but the whole pool starts getting more wavy and chaotic. That's how it is with our atmosphere - more extreme events (both "hot" and "cold") occur and in general more chaotic weather as that energy is spread in waves and troughs throughout the world.
Even more to the point, is it possible that the rate at which these extreme weather events is increasing is also increasing?
Without getting into the weeds about particular numbers, it's known that given a global temperature increase, the poles experience the majority of that change. One reason the United States has experienced so much extreme weather of late is because the northern hemisphere polar jet stream has gotten a lot more erratic, in large part because of a declining temperature delta between the north pole and its adjacent temperature bands.
Re the first question, statistical hypothesis testing requires a null state of the world that you want to test, in this case “is the global temperature changing”. What that requires, more rigorously, is some sort of assumed probability distribution that generates the data we observe. We would probably assume a normal distribution/bell curve with mean equal to the long term average temperature during the last few thousand years, or whatever period is relevant (again, im not a climate scientist), and variance deduced the same way.
To test that null hypothesis: “the temperature over the last decade isn’t meaningfully different from the long term average”, you then take your recent data, say the last and ask “what is the probability we’d see this data, assuming the state of the world we assume given our null hypothesis”. If the observed data is sufficiently unlikely to be generated by that null distribution, you say there is a statistically significant difference.
Now, That’s not the only way to analyze the data (putting it into two buckets and asking if they differ). But I don’t want to get too into the weeds without better understanding what your wondering about/where the disconnect is.
Edit: looking back on this answer, there are some glaring issues that need to be addressed, because they’re both bad analysis and you hinted at it in your question.
Obviously the issue here is that cyclical data clumps together so to speak. Sot he temporal binning i outlined here is a big issue, because you are going to get data with lower variance that you would expect.
This could conceivably be adjusted for by raising your significance threshold, though off the top of my head I’m not 100% sure how I would approach it personally.
Part of the issue for me is that I’m attempting to wrangle statistical significance into the discussion, when I haven’t properly stepped back and frames the issue properly. Like you I need to know more about the science as well in order to give a helpful answer.
Suffice to say that statistical significance is only relevant when there is a specific statistical parameter that you want to make a determination about. And in this case I’m not entirely sure what that would be.
Looking specifically at the value you referenced, I think a more useful tool you could look at would be trend decomposition.
https://www.virginiamercury.com/2020/07/17/virginias-coast-s...
Many people said no.
Both climate change and viral growth increase exponentially. Not only do we release more CO2 into the atmosphere every year, but also the growth rate accelerates.
I guess CO2 is increasing exponentially, so maybe CO2-dependent temperature change is a somewhat linear with respect to time.
Another example is in the Arctic tundra. The top layer of the ground was always frozen, i.e. a permafrost. However now that layer is melting and it releases a ton of methane. Methane causes the temperatures to rise, leading to the permafrost melting faster and more methane being released.
I'm a decades long 'climate change alarmist'.
We really don't know if the temperature is really increasing exponentially, considering the proper definition of exponential: "a value increases in proportion to its current value". Also consider that "exponential growth" doesn't necessarily mean "extremely fast"...at least in reasonable time horizons.
I and many others think that the amount of energy in our planet's atmosphere is increasing, and we also believe the rate of increase is increasing. This might be technically 'exponential', but it very well might not. It could 'just' be quadratic...which, given the 'right' constants, could be even worse.
> For reasons other than our collective output increasing exponentially?
Humanity's greenhouse gas output was growing (something like) exponentially (ie, 'very fast') for a good while, but it's probably no longer: https://ourworldindata.org/grapher/annual-co-emissions-by-re...
To your underlying, fundamental question: why is the rate of increase probably increasing? Feedback effects. To seriously get into the weeds, look here: https://en.wikipedia.org/wiki/Climate_change_feedback
In short, all chaotic but meta-stable systems, such as our planet's climate, have built in many 'tipping points', where a small change in input can have a very large change in behaviour. Under ideal circumstances, such tipping points are quite hard to identify with any precision, and virtually impossible with the most complex system in the world: earth's climate.
Even shorter: we don't know for certain, but there's a large and ever growing pile of data that shows here and now impacts of a warming climate. Per my other comment, for example: the rate at which 100, 500 and 1000 year extreme weather events are occurring.
In summary: us not knowing with certainty does NOT mean we should not make it a top priority to start reversing the things we do know are causing damage: enormous releases of CO2 and CH4.
For example, warming the climate tends to melt ice. Ice reflects sunlight back to space better than liquid water or dirt. So the reduced ice cover makes more sunlight get absorbed by the Earth. Absorbed sunlight becomes heat, which raises the temperature. The increased temperature melts more ice.
Technically all of these loops can only result in a sigmoid curve, not an exponential. The temperature won't become arbitrarily large. Trivially it can't get any hotter than the input (the sun). But in the ranges we care about (temperatures suitable for human habitation without massive adaptation and migration needed) it's effectively exponential.
Judging by the fact that for the billion years after life has dominated, Earth climate has always stayed decidedly non-Martian and non-Venusian, the evidence is strong that negative feedback loops are more powerful than the positive ones that people may publicize. I would like to see more substantiation behind such assertions.
https://quoteinvestigator.com/2021/02/01/understand-exponent...
It's not the average temperature change that is significant, its the effect of the temperature that is significant. For example, 33F vs 32F is very significant... If there are more days above freezing, which leads to extra ice melt, it doesn't matter if the average is up only a tiny bit.
https://skepticalscience.com/few-degrees-global-warming.htm
> A few degrees of global warming has a huge impact on ice sheets, sea levels and other aspects of climate.
I find it quite hard to evaluate what is being shown, when the total change in temperature over a century is smaller than the temperature difference between different parts of the room I'm currently sitting in.
Air pollution - usually linked to CO2 emissions - has a whole slew of other problems.
We absolutely have the technology to get rid of coal and oil for transport and electricity production - we need to start banning the production of new ICE cars and new coal power plants now, and tariffing any nations who don't follow.
Has there ever been a concern that we could put so much CO2 into the atmosphere as to impair cognitive function?
The poles are heating up much faster! Eg the North Pole rose 2-4c in the last 50 years:
https://en.m.wikipedia.org/wiki/Climate_change#/media/File%3...
The change is accelerating. Projections that held true in the 80s and 90s are being revised. We’re talking about 6-12 degrees Celsius warmer on Average globally in 100 years. https://en.m.wikipedia.org/wiki/Climate_change#/media/File%3... That means some days/months will be significantly warmer and our crops, food supply, water supplies and other industries won’t have adapted quickly enough to survive.
The worst case scenarios are the breakdown of civilisation and human extinction.
1. No, this is not a "cyclical perturbation", unless your cycles are long enough to include mega impact events like the ones that killed the dinosaurs[1]. The last time methane levels were this high, it was at least 800,000 years ago. The last time CO2 levels were this high was 3 million years ago. Guess what. The Earth was 2 to 3 degrees Celsius hotter back then than now. That means that parts of the Earth that are currently inhabited by hundreds of millions to billions of people will become uninhabitable.
2. Humans have never existed under the climactic regime that we are unleashing. Humans evolved over the last 400,000 years through a period of glaciation in a little cuccoon in Africa.
3. Civilization has never existed under any climactic regime other than the warm inter-glacial period from about 12,000 years ago when agriculture was first developed. Before that, it was a looong ice age that almost killed humans off completely. Before us, Earth was cyclical between glacial and interglacial periods about every 100,000 years. That cycle is now pretty much obliterated by what we did in the past 150 years.
4. Changes in CO2 concentration change have generally been very slow over Earth's history, on the order of thousands or tens of thousands of years. Such an abrupt CO2 concentration change is generally not seen short of massive volcanic activity or a planet-killer asteroid like the one that killed the dinosaurs and the majority of animal species 65 million years ago. Abrupt climate change means mass extinction for life on Earth. Buckle up, lots of shit is going to die and whole regions will turn to desert. Earth probably will not support our food production systems. Lots of us are going to die, too.
5. There has never been anything remotely like a CO2 "cycle" in Earth's climate history. There is no mechanism nor natural variation that causes CO2 to just go up and down in cycles that are predictable. If you want to educate yourself with some Science, here's a reconstruction of Co2 for the past 550 million years: http://earthguide.ucsd.edu/virtualmuseum/climatechange2/07_1...
If you can spot the cycle, I'm sure they'll award you an honorary doctorate in planetary Science, and you'll be hella famous.
[1] It's a stretch to call meteor impacts cyclical; they follow a power law distribution and are random enough that they hit about as regularly as rolling the dice. When the universe hits a hard 9, we take a beating.
The climate went through an ice age for most of the past 1 million years. As you point out in #3, an ice age glacial is infinitely worse for life on earth than mild warming. The climate prior to the Quarternary period was better for life in almost all respects. The ice age was brutal, caused mass extinctions, and nearly decimated humans as well. It also froze up so much water that virtually all of Canada and most of Russia was buried under a mile thick ice sheet. So of course, sea level was 400 meters lower than present. Much of that melting occurred with the onset of the Holocene, which has been the prevailing climate regime for only the past 12k years or so. At some point during the ice age, CO2 levels also dropped dangerously low, to 180ppm, a near record low for life's entire existence on this planet. Below 150ppm, plants die entirely. Their productivity and growth is hampered by both freezing temps and low CO2. It was so low plants could not grow at all above certain elevations that are covered in alpines today.
CO2 is not dangerous for life on earth. It is a fundamental nutrient for plant life. The optimal periods for life on this planet have all been marked by an abundance of CO2. The only mild risk from mild warming is rising sea levels. That has been documented to be holding steady at 1 foot of sea level rise per century for the past few hundred years. Much smaller than the meltwater pulse at the Younger Dryas 12k years ago. Humans have continually delt with sea level rise since we invented agriculture. It's not the doomsday event it is painted to be and the trend has not accelerated in some sort of feedback loop as was claimed 30 years ago. The trends are linear, not exponential.
I wish I could say with certainty that we have disrupted the 100K year glacial cycle. That would be incredibly good news. Unfortunately, volcanoes have a way of ruining the party. There is absolutely no evidence that a volcanic cycle cannot kick in at any moment and plunge earth in a continual regime of thick dust and particulates that increase condensation, reduce solar irradiance, and cause temps to drop by 5-10 degrees globally for the next 100K years.
> The only mild risk from mild warming is rising sea levels. That has been documented to be holding steady at 1 foot of sea level rise per century for the past few hundred years. Much smaller than the meltwater pulse at the Younger Dryas 12k years ago. Humans have continually delt[sic] with sea level rise since we invented agriculture.
That is just completely wrong. Global sea levels have been documented and reconstructed and cross-checked better than radio-carbon dating. There are still extant coastal cities that have existed for more than a thousand years, and they are all in agreement that this claim of 1 foot per century just cannot possibly true. I literally have no idea where you got this, I've never seen anyone even suggest this number. Even documented sea level rise since 1900 has been only 5 to 8 inches. Did sea level rise drastically slow down the last century? It's funny, that number, because since the 1990s the incredibly accurate modern gauges of sea level have noticed that the rate of rise has actually tripled to 3 millimeters a year and is still accelerating! That's funny, that's roughly a foot a century. So you just happen to suggest that the exact, current rate of sea level rise is the average over the "past couple centuries". Uh, no. If we were to project that 1000 years into the past, sea level would have been 10 ft lower! Corals and sediments don't lie. Sea level has been stable for 2000 years, just the perfect amount of time for modern civilization to up and build megacities on coasts the world over. Now, project that 3 millimeters per year into the future. In 1000 years, 10 feet! Goodbye all of Florida, Manhattan, and pretty much every major coastal city. But it won't be 1000 years. Things are picking up. We'll get multiple feet of sea level rise this century.
https://ocean.si.edu/through-time/ancient-seas/sea-level-ris...