Here is why.
There are thousands of scientists working on causes of global warming. They have concluded that it is humans putting CO2 and Methane into the air that creates the blanket that warms the earth. I would bet that none of them have the slightest doubt about what they have found.
The critical facts are few:
1. Once a certain temperature is reached the atmosphere takes control and causes the temperature to keep rising. This is called a "tipping point."
2. The "safe" temperature is 1.5° C rise over the recent historical temperature. It may not sound like much but it is about 150 billion billion Joules of energy becuase it means heating the whole atmosphere the ground and the oceans. It has already cause enormous problems.
3. The current rise is 0.9 and rising rapidly.
4. If we stopped all CO2 and other gasses completely, the temperature of the earth would continue to rise for hundreds of years.
5. There are many additional sources of gasses, especially methane trapped in the tundra. Methane is much worse than carbon, although it doesn't last as long. There is also methane in the ocean which will eventually be released.
6. Europe is not on track to meet the Paris goal of 2°C.
7. The US output of CO2 is increasing and this is the back breaker. It is strickly due to the presidents absolutely irrational policies. He is removing all regulations and increasing the use of coal, the worst posssible fuel. This man is crazy. He is incapable of understanding that he will go down in history (if there is a history) as the most evil man in the history of humanity.
8. Most scientists are declaring that negative emissions are necessary, that is removing CO2 from the atmosphere, but there is no unified research program to evaluate existing technology, optimize and test them or to find new technologies.
9. As a consequence it is extremely unlikely that we will meet the 2°C target, and then we are doomed, barring a scientific miracle.
10. Once we pass 2° C we will likely be on an exponential curve. If you extrapolate NASA data as of today, that is what you get.
ABOVE: NASA EARTH TEMPERATURE DATA. NOTE THE SHARP RISE IN RECENT TEMPERATURES.
BELOW: EXTRAPOLATION OF THE NASA DATA USING MANUAL BEST FIT CURVE (GREEN) BASED ON A SINGLE TERM EXPONENTIAL.
DEVELOPMENT: DASHED LINES: POLYNOMINAL 3RD AND 4TH ORDER TREND LINES CALCULATED BY EXCEL. ALL EXTRAPOLATIONS AGREE WITH OTHER METHODS OF CALCULATION IN THE NEAR TERM (UP TO 2040) AND ILLUSTRATE THE POTENTIAL FOR LONGER TERM. THESE ALSO AGREE WITH OTHER CALCULATIONS EXCEPT FOR THE WORST CASE RED DOTTED LINE WHICH EXCEEDS WORST CASE ESTIMATES BY ABOUT 4°C. NOTE THAT MOST SCIENTIFIC ESTIMATES HAVE PROVED OPTIMISTIC DUE, I BELIEVE, TO THE DIFFICULTY OF INCLUDING ALL CONTRIBUTIONS TO THE TEMPERATURE RISE.