The global average atmospheric carbon dioxide in 2018 was 407.4 parts per million (ppm for short), with a range of uncertainty of plus or minus 0.1 ppm. Carbon dioxide levels today are higher than at any point in at least the past 800,000 years.
Over the first nine months of 2015, global mean warming reached 1°C above preindustrial for the first time, as reported by scientists from the Met Office and the Climate Research Unit at the University of East Anglia.
2015 is likely to become the warmest year in more than 11,000 years (see Figure 1). This signals a departure from the mild climate of the last 10,000 years in which agriculture and human civilisations have developed and thrived.
Given the lack of action in reducing emissions over the last decade, crossing 1°C warming is an inevitable, yet highly concerning event. It is a signal from the climate system that time is running out if we are to be able to reduce emissions fast enough to hold warming below 2°C and below 1.5°C by 2100.
In the absence of policies, global warming is expected to reach 4.1°C – 4.8°C above pre-industrial by the end of the century. The emissions that drive this warming are often called Baseline scenarios (‘Baselines’ in the above figure) and are taken from the IPCC AR5 Working Group III. Current policies presently in place around the world are projected to reduce baseline emissions and result in about 3.0°C1 warming above pre-industrial levels. The unconditional pledges and targets that governments have made, including NDCs2 as of December 2019, would limit warming to about 2.8°C3 above pre-industrial levels, or in probabilistic terms, likely (66% or greater chance) limit warming below 3.0°C. Warming estimates have fallen by 0.1-0.2°C compared to the CAT’s September 2019 update. However, the reason is largely methodological changes and data updates rather than any major scaling-up of climate action.
"Well, the rate at which we're injecting CO2 into the atmosphere today, according to our best estimates, is ten times faster than it was during the End Permian. And rates matter. So today we're creating a very difficult environment for life to adapt, and we're imposing that change maybe ten times faster than the worst events in Earth's history."
-kump from ends of the world
at 2 degrees global temp rise - agriculture yields significantly less bountiful - less food for more people- hurricanes and floods, extreme weather would dramatically increase- 4x as many wildfires in california . 4 degrees all major ice sheets in the planet would begin permanent irreversible melt which means we would lose all ice no matter what we did that ice together would add at leaset 200 feet of sea levle rise to the planet - inundate every single beach youve ever been to. the entire coastline of the world on which 2/3 of all major cities exist would be unrecognizable. 4 degrees means world gdp 20-30 percent smaller than it would be without climate change- 30 percent is an impact twice as deep as the great depression in the 1930s and it would be forever. roughly 600 trillion dollars in global climate damages which is double the amount of money than currently exists in the world- agricultureal yields would be half as productive. mosquitos carrying dengue and malaria would reach around the world up to the arctic circle. currently with emissions remaining at business as usual we are set to hit 4 degrees global temperature increase by 2100- the population will be 11 billion- notes taken from years of living dangerously project with david wallace wells
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