Editing IPCC:AR6/SR15/Chapter-1 (section)

== 1.1 Assessing the Knowledge Base for a 1.5°C Warmer World ==

<div id="article-1-1-assessing-the-knowledge-base-for-a-1-5c-warmer-world-block-1"></div>

Human influence on climate has been the dominant cause of observed warming since the mid-20th century, while global average surface temperature warmed by 0.85°C between 1880 and 2012, as reported in the IPCC Fifth Assessment Report, or AR5 (IPCC, 2013b) <sup>[[#fn:r1|1]]</sup> . Many regions of the world have already greater regional-scale warming, with 20–40% of the global population (depending on the temperature dataset used) having experienced over 1.5°C of warming in at least one season (Figure 1.1; Chapter 3 Section 3.3.2.1). Temperature rise to date has already resulted in profound alterations to human and natural systems, including increases in droughts, floods, and some other types of extreme weather; sea level rise; and biodiversity loss – these changes are causing unprecedented risks to vulnerable persons and populations (IPCC, 2012a, 2014a; Mysiak et al., 2016; Chapter 3 Sections 3.4.5–3.4.13) <sup>[[#fn:r2|2]]</sup> , Chapter 3 Section 3.4). The most affected people live in low and middle income countries, some of which have experienced a decline in food security, which in turn is partly linked to rising migration and poverty (IPCC, 2012a) <sup>[[#fn:r3|3]]</sup> . Small islands, megacities, coastal regions, and high mountain ranges are likewise among the most affected (Albert et al., 2017) <sup>[[#fn:r4|4]]</sup> . Worldwide, numerous ecosystems are at risk of severe impacts, particularly warm-water tropical reefs and Arctic ecosystems (IPCC, 2014a) <sup>[[#fn:r5|5]]</sup> .

This report assesses current knowledge of the environmental, technical, economic, financial, socio-cultural, and institutional dimensions of a 1.5°C warmer world (meaning, unless otherwise specified, a world in which warming has been limited to 1.5°C relative to pre-industrial levels). Differences in vulnerability and exposure arise from numerous non-climatic factors (IPCC, 2014a) <sup>[[#fn:r6|6]]</sup> . Global economic growth has been accompanied by increased life expectancy and income in much of the world; however, in addition to environmental degradation and pollution, many regions remain characterised by significant poverty and severe inequalityin income distribution and access to resources, amplifying vulnerability to climate change (Dryzek, 2016; Pattberg and Zelli, 2016; Bäckstrand et al., 2017; Lövbrand et al., 2017) <sup>[[#fn:r7|7]]</sup> . World population continues to rise, notably in hazard-prone small and medium-sized cities in low- and moderate-income countries (Birkmann et al., 2016) <sup>[[#fn:r8|8]]</sup> . The spread of fossil-fuel-based material consumption and changing lifestyles is a major driver of global resource use, and the main contributor to rising greenhouse gas (GHG) emissions (Fleurbaey et al., 2014) <sup>[[#fn:r9|9]]</sup> .

The overarching context of this report is this: human influence has become a principal agent of change on the planet, shifting the world out of the relatively stable Holocene period into a new geological era, often termed the Anthropocene (Box 1.1). Responding to climate change in the Anthropocene will require approaches that integrate multiple levels of interconnectivity across the global community.

This chapter is composed of seven sections linked to the remaining four chapters of the report. This introductory Section 1.1 situates the basic elements of the assessment within the context of sustainable development; considerations of ethics, equity and human rights; and the problem of poverty. Section 1.2 focuses on understanding 1.5°C, global versus regional warming, 1.5°C pathways, and associated emissions. Section 1.3 frames the impacts at 1.5°C and beyond on natural and human systems. The section on strengthening the global response (1.4) frames responses, governance and implementation, and trade-offs and synergies between mitigation, adaptation, and the Sustainable Development Goals (SDGs) under transformation, transformation pathways, and transition. Section 1.5 provides assessment frameworks and emerging methodologies that integrate climate change mitigation and adaptation with sustainable development. Section 1.6 defines approaches used to communicate confidence, uncertainty and risk, while 1.7 presents the storyline of the whole report.

<div id="article-1-1-assessing-the-knowledge-base-for-a-1-5c-warmer-world-block-2"></div>

<span id="figure-1.1"></span>
<!-- START IMG -->
<!-- IMG TITLE -->
'''Figure 1.1'''

<span id="human-experience-of-present-day-warming.-different-shades-of-pink-to-purple-indicated-by-the-inset-histogram-show-estimated-warming-for-the-season-that-has-warmed-the-most-at-a-given-location-between-the-periods-18501900-and-20062015-during-which-global-average-temperatures-rose-by-0.91c-in-this-dataset-cowtan-and-way-2014-and-0.87c-in"></span>
<!-- IMG CAPTION -->
'''Human experience of present-day warming. Different shades of pink to purple indicated by the inset histogram show estimated warming for the season that has warmed the most at a given location between the periods 1850–1900 and 2006–2015, during which global average temperatures rose by 0.91°C in this dataset (Cowtan and Way, 2014) and 0.87°C in […]'''
<!-- IMG FILE -->
[[File:996ff39772146c351a403c017d2d3cb9 Chapter-1-figure-1-1024x568.png]]

Human experience of present-day warming. Different shades of pink to purple indicated by the inset histogram show estimated warming for the season that has warmed the most at a given location between the periods 1850–1900 and 2006–2015, during which global average temperatures rose by 0.91°C in this dataset (Cowtan and Way, 2014) <sup>[[#fn:r10|10]]</sup> and 0.87°C in the multi-dataset average (Table 1.1 and Figure 1.3). The density of dots indicates the population (in 2010) in any 1° × 1° grid box. The underlay shows national Sustainable Development Goal (SDG) Global Index Scores indicating performance across the 17 SDGs. Hatching indicates missing SDG index data (e.g., Greenland). The histogram shows the population living in regions experiencing different levels of warming (at 0.25°C increments). See Supplementary Material 1.SM for further details.

<!-- END IMG -->
<div id="article-1-1-assessing-the-knowledge-base-for-a-1-5c-warmer-world-block-3" class="box"></div>

<span id="box-1.1-the-anthropocene-strengthening-the-global-response-to-1.5c-global-warming"></span>