The differences between 1.5 and 2 degrees C warming
Anthropogenic (or man-made) climate change has accelerated since the Industrial Revolution. Despite research suggesting human contribution to climate change at an unprecedented rate emerging decades ago, recent studies suggest our efforts to slow or halt this phenomenon are not working. We are doing too little, and soon it will be too late. This article will consider the implications of climate change for life on Earth, and the differences between 1.5° and 2°C of global warming.
Air temperatures on Earth have been rising since the Industrial Revolution. While natural variability plays some part, modern science indicates that human activities—particularly emissions of heat-trapping greenhouse gasses—are mostly responsible for making our planet warmer.
According to an ongoing temperature analysis led by scientists at NASA’s Goddard Institute for Space Studies (GISS), the average global temperature on Earth has increased by at least 1.1° Celsius since 1880. The majority of the warming has occurred since 1975, at a rate of roughly 0.15 to 0.20°C per decade.
WHAT IS CLIMATE CHANGE?
Climate change refers to long-term shifts in temperatures and weather patterns. These shifts may be natural, but since the Industrial Revolution, human activities have been the main driver of climate change, especially through the greenhouse effect.
Some gasses in the Earth’s atmosphere trap the sun’s heat and stop it from leaking back into space, causing global warming. Many of these gasses occur naturally, but human activities increase the concentrations of some of them in the atmosphere, especially carbon dioxide, methane and nitrous oxide. Not only are human activities adding increased levels of these gasses to the atmosphere, but other activities continue to degrade the Earth, like deforestation, which further upsets the atmospheric balance. Basically we are adding more gas and not doing enough to counteract/make up for these additions.
Carbon dioxide produced by human activities is the largest contributor to global warming - by 2020, its concentration in the atmosphere had risen to 48% above its pre-industrial level (before 1750).
The image above shows carbon dioxide levels over the last 400,000 years. For the most part, they have stayed below 300 ppm but skyrocketed in the 1950s and this trend continues through the present day. Note the climate fluctuated a lot before the Industrial Revolution, though those changes were natural and much slower. Picture source.
The image above shows how the world could get warmer, or the places that will be most affected, with varying degrees of increased global warming. Note that at 1.5 degrees, many of the oceans begin to warm and we see concentrated warming in the Polar regions. By 2 degrees, we see severe warming in the same areas, as well as widespread warming of the global oceans. Picture source.
If we want to avoid the “worst” consequences of climate change, global warming needs to be kept to 1.5°C by 2100. Unless further action is taken, the planet could warm by 2°C by then, though in 2021 the Climate Action Group calculated it’ll be closer to 2.4° by the end of the century.
HALF A DEGREE - A WORLD APART
Let’s get to it. The World Resources Institute provides an excellent comparison of the main differences in 1.5° vs. 2.0°C warming with the infographic pictured below. We want to call out some of the “worst” statistics from our perspective, as they relate to the implications of climate change.
Extreme Heat - the global population exposed to severe heat at least once every five years; 14% for 1.5°C, 37% for 2° making the 2° impacts 2.6x worse
Sea-Ice-Free Arctic - number of ice-free summers; at least 1 every 100 years for 1.5°C, at least 1 every 10 years for 2° making the 2° impacts 10x worse
Species Loss: Plants - plants that lose at least half of their range; 8% for 1.5°C, 16% for 2° making the 2° impacts 2x worse
Ecosystems - Amount of Earth’s land area where ecosystems will shift to a new biome; 7% for 1.5°C, 13% for 2 making the 2° impacts 1.86x worse
Crop Yields - reduction in maize harvest in tropics; 3% for 1.5° and 7% for 2°, making the 2° impacts 2.3x worse
Coral Reefs - further decline in coral reefs; 70-90% for 1.5° and 99% for 2°, making the 2° impacts up to 29% worse
Fisheries - decline in marine fisheries; 1.5 million tonnes for 1.5° and 3 million tonnes for 2°, making the 2° impacts 2x worse
Most of these statistics are pretty jarring and paint different pictures of what life on Earth could look like, even in the next 100 years. While the impacts of 1.5° of warming are arguably better than anything warmer, we are still going to face the consequences of varying degrees of severity depending on geographic location.
The outcomes of climate change may change if we change our mentality and lifestyles, but it will require action from everyone, everywhere. 1.5°C of warming can mean risks to human security, changing ecosystems, and can endanger or even cause extirpation or extinction of some plant and animal species. 2° of warming almost guarantees near-complete coral reef death, and biodiversity would greatly suffer.
KEY COMPARISONS
Let’s explore the Key Comparisons between 1.5° and 2.0° warming in greater depth. All of the statements below are related to the differences between 1.5° and 2°. We want to note that there are a lot of comparisons we do not touch on, and the IPCC report itself is a great resource to learn more. The key comparisons we have selected personally stick out to us the most based on our education and professional and personal experiences thus far. The comparisons we are about to share just begin to scratch the surface of all the data available.
Limiting global warming to 1.5° would limit risks of increases in heavy precipitation events on a global scale and in several regions. The regions with the largest increases in heavy precipitation events include several high-latitude regions, mountainous regions, eastern Asian and eastern North America. Heavy precipitation, when aggregated at a global scale, is projected to be higher at 2° vs. 1.5°.
Risks to natural and human systems are expected to be lower at 1.5°. This difference is due to the smaller rates and magnitudes of climate change associated with 1.5°, including lower frequencies and intensities of temperature-related extremes. Lower rates of change enhance the ability of natural and human systems to adapt.
Substantially reduce the probability of extreme drought, precipitation deficits and risks associated with water availability in some regions. In particular, risks associated with increases in drought frequency and magnitude are projected to be substantially larger at 2° rather than 1.5° in the Mediterranean region.
Exposure to multiple and compound climate-related risks is projected to increase between 1.5-2° C of global warming with greater proportions of both people exposed to and susceptible to poverty in Africa and Asia. For that extra 0.5° of warming, risks across energy, food and water sectors could overlap spatially and temporally, creating new/exacerbating current hazards, exposures, and vulnerabilities that could affect increasing numbers of people and regions. Small island states and economically disadvantaged populations are particularly at risk… those who contribute the least to climate change will experience some of the greatest disruptions.
Global warming of 2° would lead to an expansion of areas with significant increases in runoff, as well as those affected by flood hazard, compared to conditions at 1.5°.
Global mean sea level rise is projected to be around 0.1m less by the end of the 21st century in a 1.5° world vs. 2°. A smaller sea level rise could mean that up to 10.4 million fewer people would be exposed to the impacts of sea level rise globally. A slower rate of sea level rise enables greater opportunities for adaptation.
Risks of local species losses and risks of extinction are much less in a 1.5° world. The number of species projected to lose over half of their climatically determined geographic range at 1.5° is 6% of insects, 8% of plants and 4% of vertebrates. At 2°, the figures are 18% insects (3x increase), 16% plants (2x increase) and 8% of vertebrates (2x increase). Risks associated with other biodiversity-related factors, such as forest fires, extreme weather events, and the spread of invasive species/pests/diseases would be lower at 1.5° vs 2°, supporting a greater persistence of ecosystem services.
The projected frequency and magnitude of floods and droughts in some regions are smaller under 1.5° of warming. The differences of risks among regions are strongly influenced by local socio-economic conditions.
Risks of water scarcity are projected to be greater at 2° in some regions. Depending on future socio-economic conditions, limiting warming to 1.5° may reduce the proportion of the world population exposed to a climate change-induced increase in water stress by up to 50%, though there is considerable variability between regions.
Reductions in projected food availability are larger at 2° than 1.5° in the Sahel, Southern Africa, the Mediterranean, central Europe and the Amazon. This suggests a transition from medium to high risk of regionally-differentiated impacts on food security between 1.5° and 2°C.
Meeting both the 1.5°C and 2°C limit will require unprecedented transformation across all economies, industries and geographies. For limiting warming to 1.5°C with no or limited overshoot, the world will need to reduce its annual emissions to 25-30 GtCO2e on average in 2030 (the world is currently on track to emit more than double this amount by 2030 (52-58 GtCO2e).
Limiting warming to 2°C would require reducing annual emissions by about 20 percent below 2010 levels in 2030; for 1.5°C, emissions will need to drop by 40-50 percent. Carbon dioxide emissions will need to reach net-zero around 2050 to limit warming to 1.5°C and around 2075 for 2°C.
Why is it necessary and even vital to maintain the global temperature increase below 1.5 C versus higher levels such as 2? Adaptation needs grow as temperature rises. Saving this half a degree will require tremendous effort, but the effort will be well worth the reward of more secure communities, ecosystems and economies. Adaptation will be less difficult, and Earth will suffer less negative impacts on:
Intensity and frequency of extreme events
Resources
Ecosystems
Biodiversity
Food security
Cities
Tourism
Carbon removal
Achieving 2˚C will avoid many catastrophic impacts from climate change, but the consequences will be significantly worse than if we can limit global warming to 1.5˚C. The purpose of this article is not to initiate fear - rather the opposite. Our goal here is to face the reality of our warming planet head-on to inspire hope in individuals to take action.
We can take action for the climate by spending our dollars consciously, by voting for people whose values are conducive to a sustainable future, by funding environmental justice initiatives, and by spreading love and appreciation for the environment around to those in our spheres of influence. We urge you to go forth after reading this, educate yourself more deeply, and commit to propelling a sustainable (cooler) future however it best makes sense for you to do so.
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