How reliable are the reconstructions and models for past temperature changes?

July 03, 2020

Understanding of climate changes during the past millennia is crucial for the scientific attribution of the current warming and the accurate prediction of the future climate change. The proxy-based reconstructions and model simulations that offer insights into past temperature changes, however, are subject to large uncertainties. Large-scale climate reconstructions are always related to the uncertainties arising from the disturbance of non-climate signals in individual proxy record, and the differences in seasonality or temporal resolution for different proxy records. Model simulations are always related to the uncertainties arising from the uncertainties of forcing reconstruction itself and the lack of some important feedback mechanisms in climate models. Nearly 20 proxy-based reconstruction and 10 model simulation datasets have been published over the past three decades; however, due to the large uncertainty in them, significant differences between different reconstructions and between reconstructions and simulations frequently happen. The uncertainty makes it difficult to have a clear picture of past climate changes, but, unfortunately a detailed evaluation of such uncertainties in reconstructions and model simulations is still rare.

The recently published paper in SCIENCE CHINA Earth Sciences, "Evaluation of multidecadal and longer-term temperature changes since 850 CE based on Northern Hemisphere proxy-based reconstructions and model simulations", were jointly written by Dr. Wang Jianglin, Prof. Yang Bao, Dr. Fang Miao, Dr. Liu Jingjing of Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences (CAS), Prof. Zheng Jingyun, Dr. Zhang xuezhen of Institute of Geographic Sciences and Natural Resources Research, CAS, Dr. Wang Zhiyuan of Zhejiang Normal University, and Dr. Shi Feng from Institute of Geology and Geophysics, CAS. The researchers evaluated the uncertainties in the published 18 reconstructions and 6 model simulations by assessing the covariance, climate sensitivity and amplitude of temperature changes in them.

The results show the uncertainty generally increases back in time as the covariances between different reconstructions or between reconstructions and simulations steadily decline back in time and becomes particularly large during the Medieval times. The results also show that climate modeling results show a shorter recovery (i.e., lag) in response to the cooling caused by volcanic eruptions and solar activity minima, and a smaller amplitude of multi-centennial temperature changes compared with those in proxy-based reconstructions.

Finally, the article gives the prospects and suggestions for future works to reduce uncertainty in large-scale climate reconstructions. Firstly, more efforts are suggested to be taken in developing long, high-quality and temperature-sensitive proxy records for the areas with sparse proxy archives (e.g., East China, Africa, Antarctic, South America, and some oceanic areas). Secondly, the reliability of reconstruction outside the instrumental period is encouraged to be strictly assessed by comparing with the low-resolution proxy records that was excluded from the current proxy network and by applying the "pseudo-proxy experiment" method.
This research was funded by the National Key Research and Development Program of China on Global Change (2017YFA0603302), and the National Science Foundation of China (41888101).

See the article:

Wang J, Yang B, Zheng J, Zhang X, Wang Z, Fang M, Shi F, Liu J. 2020. Evaluation of multidecadal and longer-term temperature changes since 850 CE based on Northern Hemisphere proxy-based reconstructions and model simulations. Science China Earth Sciences, 63(8): 1126-1143,

Science China Press

Related Climate Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Climate Insights 2020: Climate opinions unchanged by pandemic, but increasingly entrenched
A new survey provides a snapshot of American opinion on climate change as the nation's public health, economy, and social identity are put to the test.

Climate action goes digital
More transparent and accessible to everyone: information and communication technologies bring opportunities for transforming traditional climate diplomacy.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

How aerosols affect our climate
Greenhouse gases may get more attention, but aerosols -- from car exhaust to volcanic eruptions -- also have a major impact on the Earth's climate.

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

How trees could save the climate
Around 0.9 billion hectares of land worldwide would be suitable for reforestation, which could ultimately capture two thirds of human-made carbon emissions.

Climate undermined by lobbying
For all the evidence that the benefits of reducing greenhouse gases outweigh the costs of regulation, disturbingly few domestic climate change policies have been enacted around the world so far.

Climate education for kids increases climate concerns for parents
A new study from North Carolina State University finds that educating children about climate change increases their parents' concerns about climate change.

Read More: Climate News and Climate Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to