Why does adding/taking away 1° to the average global temperature create a huge impact on Earth's environment?
Adding or subtracting 1 degree Celsius to the average global temperature has a huge impact on Earth's environment because a rise or fall of 1 degree Celsius is significant considering the current temperatures [1, 3, 4]. NASA's Climate Change: Vital Signs of the Planet explains that higher temperature thresholds will adversely impact increasingly larger percentages of life on Earth, with significant variations by region, ecosystem, and species [1]. Some of the impacts of climate change are already being felt with a rise of only 1 degree Celsius [3]. For example, ice is melting faster, extreme heat, rain, and drought are happening more frequently, and 10 million people are at risk of being affected by sea-level rise [3]. A rise of 1.5 degrees would expose fewer people to the risks of the aforementioned events happening [2]. In a 2 degrees Celsius world, land could be two to three times warmer than the global average, and the Arctic could be up to four times warmer [4]. This would dramatically change the environment not just for humans but for all species on Earth.
For all living organisms, the faster climate changes, the more difficult it is to adapt to it [1]. When climate change is too rapid, it can lead to species extinction [1]. As greenhouse gas concentrations continue to increase, the cumulative impact will be to accelerate temperature change [1,2]. Limiting warming to 1.5 degrees Celsius decreases the risks of long-lasting or irreversible changes, such as the loss of certain ecosystems, and allows people and ecosystems to better adapt [1].

Even a one-degree change in the average global temperature created the conditions where human culture, civilization, and economy could thrive [2]. If the temperature naturally or unnaturally went down five degrees, human culture would have to figure out how everyone could live in, effectively, Antarctic conditions [2]. Most people would just die [2]. A few degrees of global warming has a huge impact on ice sheets, sea levels and other aspects of climate [3]. 