So here’s
the chart of HadCRUT data for the years 1980-2016. Our period of interest starts after the spike in the middle of the chart.
There are
two distinct phases post 1998. First, a lack of overall increase in temperature between
1998 and 2014 (the infamous “hiatus”). And then a record breaking strong
increase in temperature in the last two years.
The
previous post finished just after the record year of 1998. There were prophets
of climate doom, but also deniers who said the earth wasn’t warming at all. The
chart since then shows two things; firstly the hiatus gave a lot of support to
deniers, or those who argues for some kind of natural variation. It also left a
number of people who made the more alarmist claims looking slightly stupid. The
sharp increase in the last two years however demonstrates that warming is clearly
happening. Not shown on the charts is the fact that now all measurements including
satellite measures are in agreement.
We know as
naturalists that there have been significant population movements in the last 20 years. Most inspect species are moving north, or moving higher. There is a
long list of insect and bird species that have expanded their range from Europe
to the UK, and conversely we see a disappearance of many bird species from the
southern parts of their range even where there has been no change in habitat. Spring
migration is happening on average 2 weeks earlier than it was thirty years ago.
It is hard to avoid the conclusion that if all our measurements show global
temperature increasing, and all our flying creatures are behaving as if the
earth is warming, then the earth is warming. Anyone
who doubts this warming needs to explain not just why all the different methods of
measurement all show this, but why the natural world has responded as if the world is warming.
Having
established that warming is happening, the next questions – how fast and what
happens next – are much harder to call. Scientific theories do two things:
allow us to understand the past, and allow us to predict the future (even if
only in a conditional if we do this, then that will happen). Climate science is
reasonable at explaining the past, but is currently poor
at predicting the future. The chart of the temperature anomaly above is a good
illustration of this. No-one predicted the hiatus, but efforts are now underway
to explain why we have this choppy behaviour in temperature behaviour. The
emerging explanation centres round the importance of the oceans in global
warming and the role of El Nino.
Firstly
some quick calculations.
Heat
capacity of the ocean = 1.35 x 10^21 Kg x 3.993 KJ/Kg/C (specific heat capacity
of salt water) = 5.4 x 10^21 KJ/C
Heat
Capacity of the atmosphere = 5.1 x 10^18Kg x 1 KJ/Kg/C = 5.1 x 10^18 KJ/C
So the sea
holds roughly 1000x more heat than the atmosphere (if they are at the same
temperature). Hence over a long period the oceans play a key role in global temperatures.
The temperature of the atmosphere can not, over a long period, diverge too far
from its historic relationship. Thermal energy is transferred between the two.
The mechanism that seems to have a significant role in how and when this is
done is the global weather phenomenon of El Nino and its twin La Nina.
El Nino and
La Nina.
El Niño and
La Niña are opposite phases of an oscillatory climate cycle in the Pacific
ocean, and have been known about since the 1600s.
No-one really understands the mechanics of el Nino, or can predict when it will happen and how strong it will be [1,2]. Under
normal conditions, trade winds blow west from the equator keeping warm surface
water off Asia. In El Nino years these winds do not blow as hard and the warm
water flows to the American west coast bringing rain with it. La Nina is the
opposite; the winds blow strongly restricting the flow of warm water. The
consequences are far-reaching around the globe, and one consequence we are
beginning to understand is that El Nino releases heat from the ocean into the
atmosphere.
To illustrate
this I’ve taken a table of El nino/La nina years [3] divided by strength and
calculated the average global temperature anomaly in the subsequent year (ie
1998 anomaly for the el Nino in 1997-98). This is shown (poorly – mac Excel is
horrible) below
The labels on the right go from -S (Strong La Nina) to <> ("normal") to +VS (Very Strong el Nino)
This shows
generally that the stronger El Nino, the higher the temperature anomaly.
Current
thinking then is that during the Hiatus years 1998-2013 the world was still
absorbing thermal energy, but this was being stored by the oceans. The El Nino
of 2015-16 which was a very strong one has released a lot of heat and so seen a significant sharp increase in
temperature. My prediction is that in the next few years we may see
a hiatus established for a decade or so at this new higher temperature, and
then some years down the line the process repeats and the temperature moves up sharply. But that’s just my view.
Next I will look at the opinions around why the world is heating starting with greenhouse gases.
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