Climate change is caused by global warming, which is caused (the science is now clear) by the release of green house gases into our atmosphere where they trap radiation from the sun. The burning of fossil fuels is responsible for roughly three quarters of emitted green house gases. Land use changes and the use of cement accounts for the rest.
As a result of climate change, the earth is on average 0.7C warmer than the long-term mean during the period in which it has been inhabited by people - the mid-lattitudes tend to be warmer than the mean while the tropics and the poles vary.
Current projections suggest the world is set to become at least 2.2C warmer by 2050 and 4C warmer this century unless we reduce the accumulation of greenhouse gases. At 2C warmer, long-standing vaults of CO2 in the permafrost and ocean will be released, with the consequence of further emissions and warming beyond the control of our energy decisions. We dont know exactly what effect warmer climates will have, but there is likely to be an intensification of existing weather patterns, changes in ocean current circulation and changes in the combinations of plants and species and the places they can live.
Warming is not caused by changes in the sun or solar flares - those are accounted for in the climate models and cannot explain the warming we are currently experiencing.