Record highs far outpacing record lows

In a time series which has no trend, the number of record highs should be equal to the number of record lows.  Let's say you start measuring temperatures in 1950.  In 1950, the record high is, say, 25 degrees C, the record low 0 degrees C.  For a new record high to be registered, it's got to be higher than 25, and for a new low, it's got to be lower than 0.  Let's say, the next year, the high is 25.5, and the low -0.5.  These become the new record highs and lows.  But each new record makes the next record harder to reach.  If the underlying trend in the data is sideways, new record highs and record lows will become rarer, because they will be more likely to have been achieved before.  (Reminder: popular use of "record high" or "record low" as meaning "very high" or "very low" is incorrect.  The terms mean the highest high or lowest low since records began.)

So if you do see a pattern of ever higher highs, or ever lower lows, whether it's in market indices, or share prices, or climate records, it means there is a trend.  A trend doesn't mean it's higher/lower every year, it means that over time new highs/lows keep on being attained.  One year may be lower than the previous year without meaning that an upward trend has changed.  On the other hand, if successive observations do show a new pattern of falling highs and lower lows, then it becomes more and more likely that a new trend is in place.

Source: Climate Central

Daily record highs are vastly outpacing daily record lows in the U.S. We will always have warm years and cold years, but in a world without global warming, those warm and cold years would balance over time. However, that’s not what we are seeing. According to the 2017 U.S. Climate Science Special Report, after a rigorous reanalysis of GHCN stations back to 1930, 15 of the last 20 years had more daily record highs than daily record lows. The number of daily record highs outpaced daily record lows more than 4 to 1 in 1998, 2012, and 2016.

A first look at the data from NOAA/NCEI indicates that 2017 continues the warming trend, as daily record highs are beating daily record lows by a 3.5-to-1 margin so far. Below are some preliminary 2017 stats through the end of November. Visit the NOAA Daily Weather Records tool to get the daily updates on these numbers:

• Monthly record highs have outnumbered monthly record lows at a rate of 9.7 to 1

• All-time record highs have outnumbered all-time record lows 8.7 to 1

• Record high minimum temperatures have outnumbered record low minimums 4.6 to 1

As the concentration of greenhouse gases increases in the atmosphere, the ratio of record highs to record lows will likely increase even further. With no change in current emissions trends, model projections indicate that record highs could outpace record lows by 15 to 1 by the end of the century.

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The evidence that climate change is happening right now, and that we don't have to wait for decades to see its effects, is mounting.  Records aren't just falling for temperatures, but also for severity and length of droughts, rainfall events, and hurricanes.  Almost everybody, even if they are concerned about global warming, thinks it's something which will only affect our grandchildren.  But it's happening right now.  By the time our grandchildren are adult, it will be incomparably worse, unless we move aggressively and rapidly to de-carbonise our economies.  Fortunately,  technology and the costs of renewables are helping facilitate this transformation, but we need to speed the process up, and also address areas where such technological progress is not being made: air travel, cement, iron & steel, land clearing, shipping.