a. The earth isnt so big that we humans cannot have a lasting harmful impact on it. The atmosphere is really thin compared to the size of the earth. And we can have an impact to such an extent that we can be changing the composition of the atmosphere even if it is by a small amount. Carbon dioxide measurements have been made in weather baloons over the pacific from the year 1958. The graph of co2 concentration vs time shows a zig zag ascending .
http://www.climatecentral.org/news/the-last-time-co2-was-this-high-humans-didnt-exist-15938 The reason why it goes up and down once every year is because a majority of landmass is north of the equator and aslo a majority of the vegetation is north of equator. So when the northern hemisphere is tilted towards the sun the co2 level goes down, and when it is away from the sun it goes up again. However Despite the up and down you can clearly see a upward rise in the co2 concentration. and this is hard field data. Go to Galcier national park, Mount kiliminjaro, Adamello Mandron Glacier, Tschierva Glacier, Rhone Glacier and many others. If you go there and take some photographs and compare them with photographs from a couple of decades ago you will clearly see the difference. I will give the link to the source at the end.
b. Core drills were used to analyze layers of ice which accumulated over the years. The analysis of this ice gave the data of the co2 concentration at the time which the ice corresponded to. Further analysis of the isotopes of oxygen could determine accurately the temp of year in which that snow fell. If you analyze the graphs of temp vs time and co2 con vs time. Then you will realize how well they support each other. In Antarctica if you carry out this analysis you can go far as back as 650000 years.
http://www.cornwallalliance.org/2012/12/10/carbon-dioxide-and-air-temperature-who-leads-and-who-follows/. You can clearly see the seven ice ages. If you compare the present levels of co2 conc. and temp you will see that nowhere before has it risen so alarmingly. In all of 650000 years co2 level had never gone above 300 ppm and this year it is above 400. In less than a century it has gone up by 100ppm. a thing which was unheard of in 650000 years. Can you grasp the severity now ?!
c. The ten hottest years have occurred in the last few decades.
d. The predicted and observed ocean temperatures clearly show an increasing trend. When the oceans get warmer it increases the severity of storms. All time records for storms, tornadoes and typhoons were broken. If you analyze a particular Hurricane Katrina , you will see that before it hit new orleans as it passed over warmer waters in the gulf how the size got magnified alarmingly. The premise is simple , as water temperature increases wind velocity increases.
http://www.epa.gov/climatechange/science/indicators/oceans/sea-surface-temp.html e. If you analyze a graph of insurance claims over time for severe waether events. You will clearly see the increasing trend.
There are several more points but I guess its becoming too lengthy so I will sum it up. If you still act ignorant and continue with your stance then I dont know what to say. Maybe these quotes will help.
"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." - Mark Twain
“The era of procrastination, of half-measures, of soothing and baffling expedients, of delays is coming to its close. In its place we are entering a period of consequences.” - Winston Churchill