AGW Drought Migrants

Posted by: chaamjamal on: February 17, 2020

• In: Uncategorized
 
• Leave a Comment

 

[LINK TO THE HOME PAGE OF THIS SITE]

[RELATED POST ON THE CENTRAL AMERICAN MIGRATION OF 2019]

[RELATED POST ON ENSO]

 

THIS POST IS A CRITICAL REVIEW OF A NEW RESEARCH PAPER ON THE ITCZ  [LINK] CLAIMING THAT THE 2019 MIGRATION FROM CENTRAL AMERICA TO THE USA WAS CAUSED BY CLIMATE CHANGE BY WAY OF THE IMPACT OF CLIMATE CHANGE ON THE INTER-TROPICAL CONVERGENCE ZONE (ITCZ). 

 

THE CITED RESEARCH PAPER CLAIMS AS FOLLOWS

1. AGW climate change caused a contraction of the ITCZ that initiated a causation sequence as follows: ITCZ Contraction -> Drying of Neotropics -> Drying of Central America -> Social Unrest -> Mass Migration.
2. Previous work based on limited data had suggested that global cooling during the Little Ice Age had caused a a southward migration of the ITCZ.
3. However, the current research with climate models and limited observational data suggest the ITCZ does not migrate north or south in response to global warming and cooling but that it contracts and expands in response to warming and cooling.
4. To resolve this contradiction, this research undertook a paleoclimate reconstruction study from the margin of the ITCZ and combined that with existing data from across the full annual north-south excursion of the ITCZ.
5. The findings, reported in a paper published online [LINK] , are summarized in the abstract as follows: Large changes in hydroclimate in the Neotropics implied by proxy evidence, such as during the Little Ice Age, have been attributed to meridional shifts of the intertropical convergence zone (ITCZ), although alternative modes of ITCZ variability have also been suggested. Here, we use seasonally resolved stalagmite rainfall proxy data from the modern northern limit of the ITCZ in southern Belize, combined with records from across the Neotropics and subtropics, to fingerprint ITCZ variability during the Common Era. Our data are consistent with models that suggest ITCZ expansion and weakening during globally cold climate intervals and contraction and intensification during global warmth. As a result, regions currently in the margins of the ITCZ in both hemispheres are likely transitioning to more arid and highly variable conditions, aggravating current trends of increased social unrest and mass migration.
6. The [FULL TEXT] of the paper is available online where the effects of ENSO on Central American climate is acknowledged as ” (ENSO) modulates Caribbean-sourced moisture through its influence on the Caribbean Low-Level Jet (CLLJ). In El Nino events, the CLLJ is stronger and in La Nina events it is weaker, although the resultant impact on precipitation can vary. The correlation between ENSO and precipitation in our study area is weak. ENSO influence on Central American precipitation is seen mostly in the Pacific Coast and not so inland.”
7. SUMMARY: In essence, this paper provides empirical evidence in support of the widely held belief that the large number of Central American migrants who had entered the USA illegally in 2019 were climate change migrants because they were driven there by the climate impact of drought conditions brought about by a contraction of the ITCZ due to climate change. The empirical evidence consists of paleo data that show cooling trends cause the ITCZ to expand and that warming trends cause it to contract. Translated to the current AGW climate change, it implies that the warming trend had caused drought conditions in Central America by a contraction of the ITCZ and that therefore, the mass migration of Central Americans to the USA was a climate migration as claimed for example in this related post  [LINK] .

 

CRITICAL COMMENTARY

1. The paleo data studied were interpreted only in terms of temperature such that the known confounding influence of other variables such as ENSO variability   was not considered. It is also noted that paleo data contain large uncertainties that may lend themselves to different interpretations [LINK] and that comparison of results with short term observational data may be helpful in verifying the conclusions.
2. An additional consideration is that the paper limits the study of the Holocene’s six alternating warm and cool periods over about 10,000 years to the last 2000 years where only the Medieval Warm Period and the Current Warm Period remain with the Little Ice Age intervening between them. The strength of the reported findings are weakened by this limitation along with the limitation of possible causation variable to the ITCZ without consideration of SST and ENSO variability found in many of the papers in the bibliography below. These arbitrary limitations raises questions about the validity of the findings.
3. Here we present a bibliography of papers on the subject of precipitation variability in Central America where a broad spectrum of variables and conclusions are found. Many of these methods and findings are inconsistent with the what has been presented above. For example, in the Aguilar(2005) paper is reported the data and findings of a climate change workshop held in Guatemala in 2004 to investigate climate change impacts and weather extremes in Central America. The full text of this paper is available for download online [LINK] . The paper finds that a relevant climate feature of Central America is that it is adjacent to both the Pacific and Atlantic Oceans and they find that precipitation trends there are therefore strongly positively correlated with trends in sea surface temperature (SST). This correlation implies that global warming should decrease and not increase the probability of the dry conditions that are thought to have driven the migration.
4. An added consideration, seen in many papers {Chang(2015), Robertson(1998), Zhou(2001), Paegle(2002), and Gagnon(2002) are examples}, is the inclusion of ENSO variability as a factor in explaining changes in precipitation. There may be other variables in addition to SST and ENSO as for example local variables such as changes in population, agricultural practices, urbanization, and other factors. For example, development of hydro-power in Costa Rica is found to have caused significant environmental degradation that impacts the widespread availability of water {Anderson, Elizabeth etal “Quantifying the extent of river fragmentation by hydropower dams in Costa Rica.” Aquatic Conservation: Marine and Freshwater Ecosystems 18.4 (2008): 408-417.}.
5. CONCLUSION: The weaknesses of the study listed above limits the interpretation of the findings and the validity of the claim that AGW climate change caused migration from Central America by imposing drought conditions there. The exclusive focus on the ITCZ variable and the limit of the paleo data to the last 2000 years invalidates the findings particularly so in light of the Aguilar(2005) paper listed in the bibliography below.  

 

 

BIBLIOGRAPHY

1. Aguilar, Enric, et al. “Changes in precipitation and temperature extremes in Central America and northern South America, 1961–2003.” Journal of Geophysical Research: Atmospheres 110.D23 (2005). [FULL TEXT]    In November 2004, a regional climate change workshop was held in Guatemala with the goal of analyzing how climate extremes had changed in the region. Scientists from Central America and northern South America brought long‐term daily temperature and precipitation time series from meteorological stations in their countries to the workshop. After undergoing careful quality control procedures and a homogeneity assessment, the data were used to calculate a suite of climate change indices over the 1961–2003 period. Analysis of these indices reveals a general warming trend in the region. The occurrence of extreme warm maximum and minimum temperatures has increased while extremely cold temperature events have decreased. Precipitation indices, despite the large and expected spatial variability, indicate that although no significant increases in the total amount are found, rainfall events are intensifying and the contribution of wet and very wet days are enlarging. Temperature and precipitation indices were correlated with northern and equatorial Atlantic and Pacific Ocean sea surface temperatures. However, those indices having the largest significant trends (percentage of warm days, precipitation intensity, and contribution from very wet days) have low correlations to El Niño–Southern Oscillation. Additionally, precipitation indices show a higher correlation with tropical Atlantic sea surface temperatures.