Judith Curry On The Causes Of Recent Warming

By Paul Homewood

A challenging post from Judith Curry ;

 

https://judithcurry.com/2019/01/23/early-20th-century-global-warming/

Judith, in her usual thorough way, introduces much scientific thinking, both pro and anti.

But her summing up puts the whole thing in a nutshell:

In order to have any confidence in the IPCC and NCA attribution statements, much greater effort is needed to understand the role multi-decadal to millennial scales of internal climate variability.

Much more effort is needed to understand not only the early 20th century warming, but also the 'grand hiatus' from 1945-1975.  Attempting to attribute these features to aerosol (stratospheric or pollution) forcing haven't gotten us  very far.  The approach taken by Xie's group is providing important insights.

Once we do satisfactorily explain these 20th century features, then we need to tackle the 19th century — overall warming, with global sea level rise initiating ~1860, and NH glacier melt initiating ~1850.   And then we need to tackle the last 800 years – the Little Ice Age and the 'recovery'. (See my previous post 400 years(?) of global warming).  The mainstream attribution folk are finally waking up to the importance of multidecadal ocean oscillations — we have barely scratched  the surface re understanding century to millennial scale oscillations, as highlighted in the recent Gebbie and Huybers paper discussed on Ocean Heat Content Surprises.

There are too many climate scientists that expect global surface temperature, sea ice, glacier mass loss and sea level  to follow the 'forcing' on fairly short time scales.  This is not how the climate system works, as was eloquently shown by Gebbie and Huybers.  The Arctic in particular responds very strongly to multidecadal and longer internal variability, and also to solar forcing.

Until all this is sorted out, we do not have a strong basis for attributing anything close to  ~100% of the warming since 1950 to humans, or for making credible projections of 21st century climate change.

It is a point I have often made.

There is little dispute, outside of the blinkered Hockey Stick community, that the world's climate has regularly swung from warm to cold and back again.

The most recent episode, of course, was the plunge from the MWP to LIA.

Yet nobody, in my opinion, has come up with any plausible theory to explain these cycles.

Until we can explain why the world's climate changed from Middle Age warmth to the coldest times since the Ice Age culminating in the 19thC, we cannot hope to understand why it has warmed up again since.

As Judith notes, it seems that the oceans have a big role to play in this, and this is something else today's CO2 obsessed scientists have little understanding of.

We hear that the oceans have warmed up as a result of AGW. But as anybody with basic knowledge of oceanography will tell you, it is ocean temperatures which dictate the world's climate, and not vice versa.

 

And until we can fully explain what drives oceanic changes, we cannot hope to predict what might happen in the future.

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