Journal of Clinical Medicine Editorial Research Agenda of Climate Change during and after the Coronavirus Disease 2019 (COVID-19) Pandemic Hiroshi Nishiura 1,* and Nobuo Mimura 2 1 Kyoto University School of Public Health, Yoshidakonoecho, Sakyoku, Kyoto City 606-8501, Japan 2 Ibaraki University Global and Local Environment Co-creation Institute, Bunkyo 2-1-1, Mito City 310-8512, Japan; [email protected] * Correspondence: [email protected]; Tel.: +81-75-753-4456 1. Introduction The global pandemic of coronavirus disease 2019 (COVID-19) rapidly spread world- wide during the first few months of 2020. Most industrialized countries had to adopt so-called “suppression strategies” against COVID-19, aiming to greatly reduce virus trans- mission and to limit deaths and the demand for critical care services. These suppression strategies have required substantial reductions in the rate of human-to-human contact, sometimes via legally binding countermeasures including “lockdown” policies in urban areas [1]. Once such countermeasures were in place, levels of human mobility decreased dramatically, resulting in an enormous reduction in commuting owing to work-from-home policies (i.e., remote or telework). Domestic and international travel as well as other means of transportation declined drastically. It is expected that widespread use of specific methods of COVID-19 prevention (e.g., vaccination) and treatment (e.g., combination therapy using antivirals and steroids) will begin soon; however, the virus that causes COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is likely to continue circulating Citation: Nishiura, H.; Mimura, N. widely at least during the 2020/2021 winter season in the Northern Hemisphere. Research Agenda of Climate Change Such drastic and artificial changes in societies around the world have provided an during and after the Coronavirus unprecedented opportunity for the scientific community to study climate change. Global air Disease 2019 (COVID-19) Pandemic. pollution and carbon dioxide (CO2) emissions were instantaneously reduced for a certain J. Clin. Med. 2021, 10, 770. https:// duration of time [2], offering a very important chance for the general public to experience doi.org/10.3390/jcm10040770 improved air quality and reduced CO2 emissions levels. Nevertheless, the impact of COVID-19 on climate change comprises both positive and negative elements because many Received: 23 December 2020 COVID-19 countermeasures have had severely negative economic impacts. Moreover, Accepted: 13 February 2021 plans for mitigation as well as adaptation are also considerably affected by the “new normal” Published: 15 February 2021 lifestyles. Under the direction of the Ministry of the Environment, Japan, the Environmental Restoration and Conservation Agency of Japan (ERCA) has launched a strategic financial Publisher’s Note: MDPI stays neutral support program, the Environment Research and Technology Development Fund, to with regard to jurisdictional claims in support “Integrated Research on Climate Change Impact Assessment and Adaptation published maps and institutional affil- Plans” (S-18; project leader: Nobuo Mimura), beginning in the fiscal year 2020. The iations. project aims to provide up-to-date scientific evidence to assist decision-making regarding governmental policies for adaptation planning that also address climate change. As life under the new normal conditions progresses worldwide, our strategic research program should also be flexibly set to measure the scientific features of the relationship between Copyright: © 2021 by the authors. COVID-19 and climate change. In this editorial, we aim to discuss the research agenda Licensee MDPI, Basel, Switzerland. regarding this particular relationship. This article is an open access article distributed under the terms and 2. Impact of Climate Change on COVID-19 conditions of the Creative Commons Two issues must be debated regarding the impact of climate change on COVID-19. Attribution (CC BY) license (https:// First, we have begun to understand how temperature levels could have a direct impact on creativecommons.org/licenses/by/ 4.0/). human-to-human transmission of COVID-19 and how cold weather increases secondary J. Clin. Med. 2021, 10, 770. https://doi.org/10.3390/jcm10040770 https://www.mdpi.com/journal/jcm J. Clin. Med. 2021, 10, x FOR PEER REVIEW 2 of 4 2. Impact of Climate Change on COVID‐19 Two issues must be debated regarding the impact of climate change on COVID‐19. J. Clin. Med. 2021, 10, 770 First, we have begun to understand how temperature levels could have a direct impact2 of on 4 human‐to‐human transmission of COVID‐19 and how cold weather increases secondary transmission of SARS‐CoV‐2. At the moment, it is very likely that cold weather could in‐ transmissioncrease the spread of SARS-CoV-2. of COVID‐19 At [3]. the This moment, epidemiological it is very likely finding that is coldconsistent weather with could current in- creaseexperimental the spread evidence of COVID-19 indicating [3]. lower This epidemiologicallevels of transmission finding in is warmer consistent and with more current humid experimentalenvironments evidence [4]. Countries indicating in temperate lower levels zones of transmission have progressively in warmer experienced and more humidsecond environmentsepidemic waves [4 ].during Countries the summer in temperate season, zones with have a continuous progressively supply experienced of individuals second sus‐ epidemicceptible to waves infection during with the the summer novel coronavirus. season, with Analyzing a continuous the confirmed supply of individualscase data in susceptibleJapan during to infectionautumn 2020 with in the four novel urban coronavirus. cities (Sapporo, Analyzing Miyagi, the confirmedTokyo, and case Osaka), data inin Japanthe absence during of autumn interventions 2020 in and four estimating urban cities the (Sapporo, effective Miyagi,reproduction Tokyo, number and Osaka), (i.e., the in theaverage absence number of interventions of secondary and cases estimating generated the by effective a single reproduction primary case), number we observed (i.e., the a averageclear negative number correlation of secondary between cases the generated effective by reproduction a single primary number case), and we daily observed average a cleartemperature negative (r correlation = −0.31, p < between 0.01; Figure the effective 1). As a reproductionpossible mechanism number of and intensified daily average trans‐ temperaturemission on cold (r = days,−0.31, a pwell< 0.01;‐designed Figure time1). As allocation a possible study mechanism in labor of economics intensified clarified trans- missionthat people on cold are more days, likely a well-designed to spend time time in allocationindoor spaces study on in cold labor days economics [5]. In addition clarified to thatbehavioral people changes are more under likely tocold spend environmental time in indoor conditions, spaces on physical cold days mechanisms [5]. In addition could tosupport behavioral a causal changes relationship. under cold Although environmental the abovementioned conditions, physical facts mechanisms have gradually could supportemerged a as causal scientific relationship. evidence, Although it is reasonable the abovementioned to assume that facts the have way gradually in which changing emerged asweather scientific conditions evidence, will it is affect reasonable the transmission to assume of that COVID the way‐19 inremains which unclear. changing To weather control conditionsthe spread will of COVID affect the‐19 transmission infections, we of COVID-19cannot solely remains rely on unclear. warmer To controlweather the to spread curtail oftransmission. COVID-19 infections, we cannot solely rely on warmer weather to curtail transmission. FigureFigure 1. BivariateBivariate relationship relationship between between the the effective effective reproduction reproduction number number and and daily daily average average tem‐ temperatureperature in October in October 2020, 2020, observed observed in four in four cities cities (Sapporo, (Sapporo, Sendai, Sendai, Tokyo, Tokyo, and and Osaka) Osaka) in Japan. in Japan. No Notime time lag between lag between two twovariables variables was considered was considered because because the reproduction the reproduction number number reflects reflects an instan an‐ instantaneoustaneous measure measure of transmission of transmission on a given on a given day, on day, which on which temperature temperature may have may havean effect. an effect. Second,Second, moremore broadly,broadly, the the COVID-19 COVID‐19 pandemic pandemic offers offers a a uniqueunique researchresearch opportunityopportunity toto investigateinvestigate thethe increasingincreasing frequency frequency of of emerging emerging infectious infectious diseases diseases over over time time [ [6].6]. Most Most novelnovel human pathogens pathogens have have originated originated in in animals, animals, especially especially wild wild animals, animals, and and the therisk riskof emergence of emergence is known is known to be to dependent be dependent on the on thefrequency frequency of human of human exposure exposure at the at thehu‐ human–animalman–animal interface. interface. To To date, date, plausible plausible explanations explanations for for the the increasing frequencyfrequency ofof novelnovel pathogen pathogen emergence emergence include include (i) increased(i) increased local local and internationaland international travel,