The answer requires using the leftist definition of global warming.
Our planet is always warming or cooling -- the average temperature is very unlikely to stay the same over any 100-year period.
Average temperature is one way to describe the climate, and for this article I'll assume it to be a good metric (but, in my opinion, since no one lives in the average temperature, it is not a very useful statistical compilation).
To leftists, "global warming" means a gradual rise in the average temperature caused by man made carbon dioxide released by burning fossil fuels -- warming that will never stop (aka 'runaway warming').
Some leftists will ignore the obvious 1940 starting point for the ramp up of man made CO2 in the air, and claim man made CO2 started controlling the climate in 1975 -- they do this because the average temperature went down between 1940 and 1975, even as CO2 levels increased !
Leftists define the "normal" average temperature, and CO2 level, as equal to their very rough estimates of the level in the pre-industrial era -- roughly 1750.
Based on the leftist definition of global warming, as a catastrophe in progress, their claims are either a hoax, or a false cult belief, for these reasons:
(1) The climate in 2016 is unusually pleasant and stable, based on the average temperature, humidity, precipitation, the accumulated cyclone energy index and sea level rise trends ... along with climate proxies such as food crop production and 'greening' of our planet -- both improving from more CO2 in the air.
(2) Humans can not predict the future climate, not even one year in the future,
(3) The small change in average temperature since 1850, based on very rough estimates, is perfectly normal for our planet,
(4) The temperature in 1750 was unusually cool -- part of several cool centuries from 1300 to 1800, according to climate proxies and a few real-time measurements -- and did not feel "normal", according to the writings of people who lived during the cold spells.
(5) Climate change had been natural for 4.5 billion years -- CO2 did not suddenly replace all natural causes of climate change in 1975, and become the sole climate controller, and
(6) The average temperature had a flat trend from 2003 to 2015, even as huge quantities of CO2 were added to the atmosphere.
The leftist definition of global warming is wrong for many other reasons:
(1) Average temperature and CO2 levels for 99.999% of Earth's history have no real time measurements -- "normal" can't be defined based only on measurements made during 0.001% of Earth's history.
(2) There is no scientific proof CO2 has ever been a climate controller during any part of Earth's 4.5 billion year history, and much evidence that CO2 levels rise hundreds of years AFTER oceans warm from natural causes (meaning CO2 was not the cause of the ocean warming).
(3) The current CO2 level of about 400 parts per million is not far from the lowest estimated CO2 level ever (during peak glaciation 20,000 years ago, when Canada was under ice, and the CO2 level was estimated to be under 200 ppm).
Climate history scientists believe CO2 levels have been up to 10x or 20x higher at their peak in Earth's history -- with no evidence of runaway warming at that time.
SUMMARY:
The leftists claim 4.5 billion years of natural climate change suddenly ended in 1975, and then man made CO2 took over as the climate controller.
There is no scientific proof this is true, and not even an explanation of what could cause that to happen -- there are only feelings and unproven beliefs.
There is no evidence the climate in 1750 was "normal", and much evidence that 1650 to 1750 had an unusually cool average temperature.
CO2 measurements from Mauna Loa over the past 60 years show humans have increased the concentration of CO2 in the atmosphere by only one part per 10,000, or +0.01%.
People like me who doubt this minuscule +0.01% CO2 concentration increase in the past 60 years was the primary cause of a small amount of global warming since 1940, are often character attacked and ridiculed -- we are called "science deniers.”
Leftists do not debate their "climate change" beliefs -- climate change is their 'secular religion', not science.
Anyone who questions their climate models, whose climate predictions have been wrong for 40 years so far, is their enemy.
I have questioned their scary, and wrong, global warming predictions since 1997.
The average temperature of our planet was in a flat trend between 2003 and 2015, even as CO2 levels increased a lot.
Did your favorite media source ever tell you that?
The leftist response to the 2003 to 2015 "pause" was to gradually "adjust" historical temperature data every year until the flat trend eventually became a slight rise.
Global warming predictions of runaway warming get attention and grants for scientists, and allow politicians to increase government control over private sector energy use.
The very small temperature rise since the late 1800s was good news for humans, after many cold centuries, and not the bad news claimed by leftists.
The centuries from 1300 to 1800 were believed to have been unusually cool, based on climate proxy studies, so the slight warming (+1 degree C.) since then was good news!
Of course good climate news does not get attention, and government grants, and could never be the catalyst for a multi-trillion dollar "green" industry.
“The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary.”
H.L. Mencken
One of the "hobgoblins" is the false claim of a coming climate change catastrophe.
The global warming narrative, of a coming climate catastrophe, is a leftist hoax.
The current climate is good and has been getting better in the past 150 years -- the Earth is actually greening, according to satellite pictures.
Earth does not need saving from carbon dioxide -- more CO2 in the air -- triple to quadruple the current level -- would be great news, accelerating green plant growth, with little or no effect on the temperature.