Why We Care:
It isn’t just about feeling a bit warmer sometimes; it is a climate crisis.
In fact, there have been much more dramatic changes in the climate over Earth’s long history, even in the history of our species, but the latter occurred when we were more mobile hunter-gatherers and much fewer in number.
Our modern civilization developed with a climate that could sustain farming, fishing and settlements in particular parts of the world since the last ice age ended.
Since the Industrial Revolution and the large increase in population of the last two centuries, we have become dependent on technologies and infrastructure that are not easily moved.
Now more than 700 million people live on coasts and are threatened by sea level rise.
Even modest changes in average temperature can change where we can live and disrupt our ability to feed billions of people.
If we have to move major segments of our infrastructure, our farming, our coastal cities, there’s often no place to move to and no way to pay to get our stuff there when there is!
Heat
While it isn’t just about the rise in temperature, in fact, heat kills people. There are the direct effects of high temperatures on the body and mind as well as indirect effects (for example, changes in disease vectors like ticks and mosquitos).
Biosphere disruption
Our food supply depends on avoiding crop failures due to heat and drought, and altered insect and pollinator (e.g., bees and butterflies) life cycles. Many species that have co-evolved for a certain climate may not be able to respond to the new climate at the same rate. This may result in a deadly mismatch.
For example, animals can move quickly further polewards (north in the northern hemisphere, south in the southern) or to higher elevations than plants can (until they run out of mountain!), but the plants and trees they depend on may take much longer to change their range and distribution. And this is happening already: the Intergovernmental Panel on Climate Change (IPCC) AR6 2022 reports that half of species assessed globally have moved polewards or to higher elevations on land. There is just so far they can go before climate change again catches up with them, and in the meantime this can disrupt ecosystems.
As another example, migrating birds may arrive too late for the caterpillars they eat if the caterpillars mature earlier in the season. And both may be out of whack with the plants the caterpillars eat, and if the caterpillars do become butterflies, the butterflies may be out of synch with the flowers they depend on and that depend on them for pollination. There is more in the section on the biodiversity.
Oceans
Oceans hold more heat than dry land. Of course, most of the Earth is covered by oceans, but importantly water has a higher “specific heat” than air or the land surface, so large bodies of water are generally more affected than land masses.
A high specific heat means it takes longer to heat up water, and that once it absorbs a certain amount of heat, the water holds the heat longer. This is of grave concern because of the effects on ocean ecology. Half of our oxygen is from photosynthetic plankton and many food stocks, like fish and shellfish, and the coral reefs that many species depend on, are impacted by changing ocean temperatures. In fact 90% or so of the increased heat is absorbed by the vast oceans and 2022 was the warmest ocean temperatures recorded since monitoring began..
The movement of warm water to colder areas in major ocean currents warms local land masses (like western Europe and the northeastern United States). Disruptions in these ocean currents could be catastrophic, resulting paradoxically in colder winters, despite overall global warming. This could be devastating to the economies and the food supply in those regions, and impact food supplies and prices globally.
A large proportion of the human population and economy is coastal. Rising oceans can disrupt civilization and cause economic disaster and displacement of populations.
The oceans are indeed already rising.
Global mean sea level evolution from January 1993 to September 2021.Data source: AVISO altimetry
Why are oceans rising? Skeptics are right: melting sea ice doesn’t change sea levels. After all, the ice is already in the ocean. When ice melts in your glass, the glass doesn’t overflow.
However: Melting ice in glaciers on land, where the melt water ends up in the seas and oceans, does raise sea levels. And this is clearly happening. It is now estimated that the water locked up in currently melting Greenland ice will raise ocean levels by almost a foot by the end of the century. A foot doesn’t sound like much, but in coastal areas areas that are at sea level, it can be devastating.
But hold on. It may be a lot worse. In the summer of 2022 it was found that the Thwaites glacier in Antarctica, the widest on Earth, is melting faster than anticipated, may break up over the next few years, and may result in over 3 feet of sea level rise. That would be terrible for coastal communities around the world.
It isn’t just melting glaciers that cause sea level rise. Hot water expands. Adjacent water molecules are held together loosely by relatively weak “hydrogen bonds” that form and break apart rapidly (unlike the lattice formation in ice where water molecules are less free to move about). The hotter the water is, the more the hydrogen bonds break, the more rapidly water molecules move, so the water expands. While a relatively small effect, over an ocean of water it adds up to a big deal.
Water acidity is also well understood. CO2 + H2O (carbon dioxide and water) become H2CO3 (carbonic acid). Also, other compounds like sulfur dioxide from fossil fuel combustion contribute to acid rain. This is also a small effect with big consequences. Even a modest increase in water acidity can dissolve calcium compounds (calcium carbonate) in the shells of ocean creatures (releasing CO2!), including some shellfish (laboratory studies indicate that different species may have different vulnerability) and coral reefs, altering their ability to survive, and so alter the ecosystem, in ways that can become devastating.
There are other problems as well. For example, the bleaching of coral reefs is due to the loss of photosynthetic organisms, which are symbiotic with the coral, due to higher temperatures. The loss of viable coral reefs is not just about lost tourist dollars and less fun for divers, but affects the ecosystem that relies on the coral, and so directly and indirectly the livelihood and food supply of hundreds of millions of people.
Severe weather: droughts, fires, rain, floods, hurricanes
The suffering from these for individual humans and other life, as well as the potential effects on populations and the economy with cycles of disruption, is obvious.
More water evaporates into the air from the ground where it is hot and dry, more so as the temperature goes up, and warmer air holds more water vapor. This water in the atmosphere rains down in areas where it had normally rained more before global warming. So, the dry areas get drier, the wet areas get wetter.
Droughts and fires:
Even in arid areas, there is dew, some moisture in the air. With higher temperatures, rather than dew settling, it evaporates more quickly and completely, and is lost to the atmosphere locally, causing drier conditions in arid areas.
The drier conditions lead to more dry “fuel” (grass, shrubs, trees), resulting in more and larger, out of control, wildfires.
Droughts are not new. At this point is seems hard to say increased global temperatures are causing droughts, rather than exacerbating them.
However, this is one of the areas where there can be relatively fast and catastrophic “tipping points” made more likely by climate change. Almost one-fifth of the global human population lives in south Asia, and they depend on snowpack in the Himalayas for their water. It is not totally clear how the loss of snowpack and glaciers will impact the water supply, depending on patterns of snow and rainfall, complex river systems, and other local factors, but the potential for disaster is vast.
If that seems a distant concern, keep in mind what a connected world we live in and how disruptions will affect nations and economies, first locally, then regionally, then globally. This is a recurrent theme.
Rain, floods, hurricanes:
The water collected in the warmer air goes somewhere. Following the normal air circulation of the atmosphere (generated by the tilt of the Earth with more sunlight in the area between the Tropics of Cancer and Capricorn), it goes where rain normally occurs more, where there are more storms and hurricanes. More water is dumped there causing floods (exacerbated by higher sea levels in some areas like Miami, that floods in places already at high tides).
Hurricanes do not seem to be occurring more frequently, but there are stronger, more devastating hurricanes now than before. The power of a hurricane is increased by warmer waters from global warming. That higher energy due to the increased heat content of the ocean water is transferred to the hurricanes.
World Weather Attribution reports on attribution of the contribution of climate change on extreme weather events. From their website: “Extreme Event Attribution … was assessed to yield reliable estimates of changing risks of extreme weather by the US National Academy of Sciences…The World Weather Attribution (WWA) initiative, a collaboration between climate scientists at Imperial College London in the UK, KNMI in the Netherlands, IPSL/LSCE in France, Princeton University and NCAR in the US, ETH Zurich in Switzerland, IIT Delhi in India and climate impact specialists at the Red Cross / Red Crescent Climate Centre (RCCC) around the world.”
Additional effects
Climate change can lead to the spread of infectious disease to new areas, to extinctions and decreased biodiversity, including species and ecosystems we depend on, and increase social injustice.
Thats’ why we care. The survival of civilization and the health, well-being and lives of billions of people depend on us taking action to prevent the worst outcomes.