|Carbon Diode Concentration, from ice-core records and recent observations.|
First, let's just look at the change in CO2 concentration, say during the last 1000 years. The recent increase to over 400 parts per million is dramatic. Increased concentrations of this (and other) greenhouse gases since the Industrial Revolution have resulted in average temperature increases of about 1.1 degrees C. This rise continues at about 0.2 degrees per decade. The IPCC has recommended trying to limit the temperature rise to 1.5 degrees.
We are already observing the effects of climate change in rainfall patterns, extreme weather events, sea-level rise, forest fires, etc and these will obviously get worse at the greenhouse gas levels rise. IPCC points out that the effects are significantly worse when the temperature rise reaches 2 degrees. Their models indicate that a 45% reduction in emissions is required by 2030, (from 2010 levels), to limit warming to about 1.5 degrees, with net 0% emissions by 2050. To limit the average rise to 2 degrees requires a 25% reduction in emissions by 2030, increasing to zero emissions by 2050. Furthermore, the general climate models can not accurately predict various tipping points that may cause abrupt worsening of global warming effects. At present it seems that some indicators of climate change(e.g. reduction in Arctic ice cover) are developing more rapidly than IPCC models predict. Beyond 1.5 degrees it's increasingly difficult to predict the socio-economic effects of climate change, but they are likely to be dire.
On the present trajectory, within one generation (about 20 years) we will reach the 1.5 degree limit. A huge effort is required in many areas, including energy generation, transport, agriculture and manufacturing, to cut greenhouse gas emissions. Even more effort is needed if we delay. Solutions do exist!
To quote from a recent TAI report:
Immediate and sustained action to reduce greenhouse gas emissions is needed is to avoid the most dangerous climate impacts. The cost of action should not be exaggerated to try to distract from the large and increasing cost of inaction.
I'm not a climate scientist but I understand the scientific method (e.g. my previous posts on this site). Please understand that climate science uses exactly the same approach that characterises all our technical progress since ancient history. Hence if (say) you use a smart phone and don't believe it works by magic, you should believe in climate science!