Then there is the question of 'statistically-significant' warming - has it happened?
When this subject is discussed by individuals, it's not always clear what they mean. For this article, a statistically-significant global warming means that the linear trend (slope of the trend line) is likely greater than zero with 95% statistical confidence (i.e. the 95% error bars do not include a possible 0.0 or negative temperature degree slope).
Or, using a very simplified example, a calculated (estimated) linear global warming trend, of say 1.50°C/century, is not statistically-significant if the error bars are at ±1.55°C. If the 1.55 error is subtracted from the 1.50 linear trend, an actual possible trend could potentially be negative, not positive, nor even zero.
For more about statistically-significant global warming, there is an expert discussion here. Using the 2013 year-end major temperature datasets listed in that expert discussion, the above grid table (click on to enlarge) represents the lack of statistically-significant warming for each dataset. (When reading the WUWT article, remember that a statistically-significant warming trend does not necessarily mean that it is a climate-significant trend.)
In summary, the table depicts (for those listed climate records) the lack of statistically-significant warming since mid-1997. That's 16+ years. For two of the datasets, it's now up to at least 20 years without a statistically-significant global warming trend.
So, what's that gotta do with '4 Hiroshima bombs per second', you ask?
Well.....the CAGW dead-enders would like everyone to forget about the actual empirical evidence and statistical facts, and instead, focus on the concept that possibly global warming is adding some 4 Hiroshima bombs of energy per second. They imply that this added energy rains down untold destruction from pole-to-pole.....a classic recent example of this hyperbole is described by this journalist.
Amazingly, the dead-enders conveniently forget to mention the science facts, such as the Sun blasts Earth with energy that is equivalent to 1,950 Hiroshima bombs....per second. When one does the arithmetic (86,400 seconds per day times 1,950 H-bombs/second), that's approximately 169 million Hiroshima bombs of natural warming per day.
Thus, when putting hyperbole into factual context, it helps explain why anthropogenic warming might not be making any statistically-significant impression on nature. And, obviously, the over-the-top hyperbole has made little impression on Americans; not so much on Europeans either.
Data source for table.