Global Warming — Human Impact
This essay covers the impact of humans on global warming and the future impact of global warming on humans and the planet as a whole. The previous essay, “Global Warming — The Historical Perspective” discussed how CO2 levels in the atmosphere impacted the climate over the past 500 million years. During that time, living creatures removed CO2 from the atmosphere and deposited it as coal, oil, and the natural gases that they create. CO2 levels in the atmosphere were reduced from 5000 parts per million (ppm) to 200 ppm and the average global temperature dropped from 28C to 14C. We saw that in the past the temperature was closely correlated with the CO2 in the atmosphere. We can use that information to extrapolate the impact of humans putting that CO2 back into the atmosphere as we burn fossil fuels.
Human Activity
We split off from the apes about 5 million years ago and started walking upright. We lived in small hunter/gatherer groups and had very little impact on the planet. We evolved during the Pliocene and Pleistocene eras to handle both tropical and ice age conditions. The current theory is that modern man (Homo Sapiens) emerged from Africa about 200,000 years ago and spread from there to the rest of the planet replacing all the previous species of hominids. This “invasive” species was a ferocious hunter with a huge brain and excellent weapons and was responsible for significant extinctions in large fauna that had no defense against man’s intelligence and weapons. It is notable that the extinction of the large fauna in North America and Australia coincides with the arrival of Homo Sapiens.
About 20,000 years ago, we developed agriculture and what we now call civilization. Our agriculture has had a huge impact on the environment. The fertile crescent that was the cradle of civilization is now a desert. In the places where we live, forests are cut down for fuel and lumber and replaced with fields and gardens; swamps are drained; deserts are flooded; streams and dammed; and oceans are pillaged. Natural habitat for animals and plants has been destroyed everywhere and we are actually in the middle of one of the largest extinction events in the planet’s history, and it has been caused by us. However, it is this activity that has made us successful and enables us to house and feed almost 8 billion of us.
By a couple of hundred years ago we had burned down most of the forests in the civilized world and were looking for new sources of energy to power the steam technology that was driving the first part of the industrial revolution. We discovered coal. Burning it produced the heat to create the steam and released the ancient carbon back into the atmosphere as CO2. Coal would also go on to become the main fuel to create the electricity that would power the second half of the industrial revolution. But coal was dirty and not very efficient. Oil was much cleaner and much easier to use. Soon a huge automotive industry was consuming huge quantities of oil and pumping enormous quantities of fossilized carbon back into the atmosphere.
There is no doubt that human activity is working to unleash the energy stored in fossilized hydrocarbons and release the carbon back into the atmosphere as CO2. This will certainly cause the average global temperature to rise. What damage will this do.
Damage
In the previous essay we looked at the historical record. We can use this information to estimate the potential damage of adding the CO2 stored in fossil fuels back into the atmosphere. In the worst-case scenario, we would put it all back, all the coal and oil. If we did this, it would take us back to the conditions that existed during the Cambrian era, over 500 million years ago. CO2 levels were about fifteen times their current level and the global average temperature was about 28 degrees Celsius. There were no polar ice caps, sea level was 70 meters higher, and tropical conditions prevailed globally. We don’t have any records of the weather conditions at this time, but they were probably more extreme. However, this was the time when plants and animals first conquered the land, so the conditions did favor life, but definitely not 8 billion human lives.
At the end of the Paleocene, about 50 million years ago, the CO2 levels were about ten times what they are today, and similar conditions prevailed. The poles were free of ice caps, and palm trees and crocodiles lived above the Arctic Circle and much of the continental North America, Europe and Asia had a tropical environment. The Paleocene-Eocene Thermal Maximum (PETM) is the peak at about 50 million years ago with the average global temperature near 28C again. We have no records of what the weather was like, but this was the beginning of the age of mammals, so although it was very hot, it couldn’t have been too bad. If we did return to Paleocene or Cambrian conditions, it is possible for humans to continue to survive in terms of temperature and weather, but probably not all of us.
The biggest problem for humanity will be the rise in sea level. With the ice-caps gone it would rise 70 meters, flooding most of the world’s major cities. However, changes like this in the past have typically occurred gradually over time. Based on the changes we’ve seen during the recent ice-age cycles, we’ve probably got at least 1000 years to work with and can adapt to the rise in sea level, although it will be very disruptive since the majority of people currently live near the sea. The maps below show the extent of the damage with a 70m rise in sea level (source: Flood Map: Elevation Map, Sea Level Rise Map)
The east coast of North America is completely wiped out, Holland and Denmark disappear, England and Ireland are hard hit, other parts of Europe don’t do well, large parts of the Ukraine and Kazakhstan are under water, the Amazon and Uruguay rivers become part of the sea, Senegal is wiped out, China loses a lot of territory, the Philippines, Malasia, Cambodia, and Japan are hard hit, and Bangladesh disappears completely. Even if this flooding is spread out over 1000 years, the disruption to human society will be huge. There will be mass migration, wars, famines, and disease. However, I think human civilization will survive the transition.
High temperatures will also be problematic making it difficult for people to live near the equator. This will also drive mass migration like the rising sea levels, but once more humans are flexible and will survive the transition, especially since the large areas that are currently uninhabitable in Canada, Siberia, and Antarctica will become available.
Certainly, the climate will change and there will be more severe weather events, but the Earth has survived these before. As a species, we’re pretty adaptable and should be able to adapt to the new high temperature, high sea level environment. There will certainly be challenges. We’ll still have all those mouths to feed.
There is still the possibility that crossing a specific tipping point could bring about change much more rapidly, but we don’t actually have any historical example to back that up.
The Bright Side
On the bright side we’re not losing a lot of agricultural land to flooding and global warming would open up a huge landmass to agriculture that is currently occupied by Ice, Tundra, and Boreal Forest. This includes northern Canada and Russia, Alaska, Greenland, and Antarctica. That’s a lot of land. Large swaths of Asia, Africa and Australia that are now desert could benefit from a more humid environment due to increased temperature combined with higher sea levels. Increased CO2 will make life easier for plants and this may help us produce more food for our growing population. This is of course speculation on my part but perhaps someone should look at the potential benefits of higher temperatures and CO2 levels.
Intergovernmental Panel on Climate Change (IPCC)
What is the official view on climate change. The IPPC have been studying climate change since 1988 and have issued numerous reports. The information below comes from their 2023 Synthesis Report. It’s a excellent summary of the accepted research on the topic. A large part of the report is dedicated to showing that human activity is responsible for the addition of greenhouse gases into the atmosphere that in turn have caused a temperature increase. They make a very convincing case and even some climate change deniers now admit that this is true.
In the report they consider five scenarios. These are summarized in the table below.
The scenarios are named SSPx-y, where SSPx indicated the “socio-economic pathway” (which I think is the emission levels) and “y” denotes approximate level of warming (in watts per square meter) in the year 2100. The temperature and sea level changes are calculated from the average temperature from 1850–1900. If we continue doing what we’re doing now (SSP2), by 2100 the temperature will be 2.7C hotter and sea levels will have risen by 75cm.
There will be more extreme weather, heatwaves, and flooding, but I’m sure we can deal with that. The report says…
“Human-caused climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened…”
The report itself does not provides the detailed numbers to back up these claims, however I did find a 2409 page report “Climate Change 2021 — The Physical Science Basis” that does address the extreme weather issue. I didn’t read all 2409 pages, but in terms of extreme weather, they have seen a definite increase in temperature (1oC on average), regional increases in rainfall and flooding, some regional increase in drought, significant increase in wildfire frequency and ferocity, and a definite increase in glacial melting. There doesn’t appear to be a significant increase in storm severity (cyclones, hurricanes, tornados, thunderstorms). For example, with respect to tropical cyclones (TC) it says…
“There is low confidence in most reported long-term (multi-decadal to centennial) trends in TC frequency- or intensity-based metrics due to changes in the technology used to collect the best-track data. This should not be interpreted as implying that no physical (real) trends exist, but rather as indicating that either the quality or the temporal length of the data is not adequate to provide robust trend detection statements, particularly in the presence of multi-decadal variability.”
I would translate this to mean… “we haven’t seen any measurable increase in tropical cyclones”.
With respect to sea level rise, in the worst-case scenario, the report predicts a sea level rise of 2 meters by 2150 and 7 meters by 2300. This is pretty much in line with my conjecture that we will have a fair bit of time to adapt to increasing sea levels.
The Deniers
What do the climate change deniers have to say. There are of course various levels of denial. There are still those that don’t believe global warming is occurring; those who admit it’s occurring but don’t think it’s caused by us; those who admit it is occurring and is cause by our CO2 emissions but think that the effects are greatly exaggerated. A good summary of their views can be found in an ICSF document — “An Overview of the Latest Climate Science for Policymaker”.
One argument is that the effect CO2 is currently saturated and will not increase if we add more CO2 into the atmosphere. This is not supported by historical data that clearly shows much higher temperatures when the CO2 levels were higher. Another is that CO2 levels increase because the temperature increases, rather than the other way around. This argument is not very convincing since there is no doubt what’s causing the current increase in CO2. We’re burning coal and oil and you can actually calculate how much CO2 we’re adding. It could be that in the past some CO2 fluctuation is due to temperature rise, since warm oceans hold less CO2 than cold ones, but most of the historical fluctuations in CO2 are directly correlated with geologic or biological events. There are also arguments that claims a doubling in CO2 would cause a temperature increase of 1.1C not 2.3C as is reported in the IPCC models. Even if this were true, it only marginally diminishes the scale of the problem.
The deniers may have a point in the fact that some extreme weather events like hurricanes, tornados, and tropical cyclones have not been increasing. However, other extreme weather events like extreme temperature, wildfires, rain, sea level rise, and melting ice at both poles and the glaciers, are definitely occurring.
Conclusion
Human activity is pumping CO2 into the atmosphere which has caused and will continue to cause an increase in the mean global temperature, which will in turn change the climate. It is pretty clear that this will cause problems, but not obvious that this will cause a catastrophe of doomsday proportion. In the past the Earth had 15 time the CO2 in the atmosphere than it does today and it survived and even thrived. If we continue on our current path and pump all the CO2 back into the atmosphere, the mean global temperature will increase to the historic levels of the Cretaceous period (28C) and sea-levels could rise by up to 70 meters, flooding most of our cities. However, this will likely take thousands of years to happen and give us time to adapt.
This adaptation will not be problem free. The increase in temperature and sea levels will drive mass migration, wars, famines, and disease. Billions of people will be impacted. It may not be doomsday, but it will certainly unleash immense carnage. However, I think human civilization will survive the transition. The loss of living and agricultural space in costal and equatorial regions will be offset by gains in Canada, Siberia, Greenland, and Antarctica.
We can avoid this problem if we stop burning fossil fuels and certainly reduce its impact if we reduce our emissions. This will give us more time to adapt to the increasing temperature and rising sea levels. But more importantly, the practice is unsustainable since these are non-renewable resources that are too valuable to just burn. We have to look for sustainable sources of energy that can support our population without polluting the planet.
